Is heat index the same as 'real-feel' temperature?

They're cousins, not identical twins. Heat index is the official NOAA version using only air temperature and humidity. 'Real-feel', 'apparent temperature', AccuWeather RealFeel, Canada's Humidex, Australia's Apparent Temperature — those often add wind speed and solar radiation for a fuller picture. They generally agree within 2 to 3 degrees in normal conditions and drift apart in extreme heat. This calculator uses NOAA, which is what most international heatwave warnings align to.

Above what heat index is it dangerous to exercise outdoors?

NOAA bands give you clean targets. Above 32 degrees C (90 F) you're in 'Extreme Caution' — fatigue, cramps, and heat exhaustion become real possibilities. Above 39 degrees (103 F) is 'Danger' — heat exhaustion is likely. Above 52 degrees (125 F) is 'Extreme Danger' — heatstroke is imminent. As a practical rule: reduce intensity above 32 HI, and just don't train outside above 41. Move to early morning, an air-conditioned gym, or a pool — your training quality drops in extreme heat anyway.

Does this account for direct sunlight?

No — the Rothfusz formula assumes you're in shade. Direct sun adds another 5 to 10 degrees to what your body actually feels. That's why noon-to-3 PM outdoor work in Pakistani or Gulf summers crosses into genuinely dangerous territory even when the official forecast looks merely 'hot'. If you're in full sun, treat the displayed heat index as a comfortable lower bound, not the real number.

What's the difference between heat index and wet-bulb temperature?

Heat index is a comfort and safety estimate; wet-bulb is a physical measurement. Wet-bulb temperature is what a thermometer reads when wrapped in a wet cloth and ventilated — it captures the absolute lowest temperature evaporative cooling can reach in that air. A wet-bulb above 35 degrees C is the survivability threshold beyond which a healthy human cannot cool themselves no matter what, even in full shade. Parts of Jacobabad and the Gulf cross this threshold for hours every summer. That's the number atmospheric scientists actually worry about.

Why does my country's forecast app show a different number?

Different national weather agencies use different 'feels like' formulas — Humidex in Canada, Apparent Temperature in Australia, AccuWeather RealFeel almost everywhere — and they agree within 2 to 3 degrees in comfortable conditions but drift apart in extreme heat. This calculator uses the NOAA standard, which is what the US National Weather Service and most international heat-warning systems align to. If your forecast disagrees by a couple of degrees, both are probably 'right' within their own model.

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Find the 'feels like' temperature from air temperature and humidity. Live weather for your country.

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Heat Index Calculator

Generated on May 23, 2026

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Air Temperature

Relative Humidity

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Heat Index Result

Feels like 37°C / 99°F — Extreme Caution

Generated

5/23/2026

Feels Like (Heat Index)

37°C

99 °F

Extreme Caution

Air: 32°C · 89.6°F · 60% RH

Heat cramps and heat exhaustion possible. Limit strenuous outdoor activity, especially midday.

Why does humidity make it feel hotter?

Sweat cools your body when it evaporates from your skin. High humidity slows that evaporation, so heat is trapped — the air feels hotter than the thermometer reads. The Heat Index (or "apparent temperature") combines temperature and humidity into one number that better reflects physiological strain.

Heat-index estimates are based on shaded conditions and a light wind. Direct sun, calm air, or strenuous activity can push the felt temperature 5–10 °C higher.

Step-by-step calculation

Formula

HI ≈ Rothfusz regression (NOAA): HI = c₁ + c₂T + c₃R + c₄TR + c₅T² + c₆R² + c₇T²R + c₈TR² + c₉T²R²

1Temperature = 32°C = 89.6°F
2Relative humidity = 60%
3Within the Rothfusz regression's valid range — applying full NOAA polynomial.
4Heat Index = 98.7°F = 37.1°C → Extreme Caution

Quick Answer

Find the 'feels like' temperature from air temperature and humidity. Live weather for your country.

Overview — Heat Index Calculator

Health

Formula

HI (°F) = c₁ + c₂T + c₃R + c₄TR + c₅T² + c₆R² + c₇T²R + c₈TR² + c₉T²R²,  where T is air temperature in °F and R is relative humidity in %.

32 °C with 70% humidity (typical Karachi summer afternoon) feels like 38 °C — entering NOAA's 'Extreme Caution' band.

35 °C with 60% humidity in Lahore feels like 45 °C — beyond what most outdoor workers can sustain safely without breaks.

Dubai at 40 °C with low 25% humidity feels like only ~39 °C — dry desert heat is more tolerable than humid coastal heat at the same thermometer reading.

By Muhammad Salman SaleemUpdated: May 23, 2026MethodologyFree, no sign-upRuns in your browser — your data stays private

From the editors — what to know before you start

It's 2 PM in Karachi, the thermometer says 35 degrees, and you're trying to figure out why every step from your car to the office door feels like wading through soup. The honest answer is: your forecast is lying to you a little. Air temperature alone doesn't capture what the body actually feels — humidity does most of the talking. When the air is already heavy with moisture, your sweat can't evaporate, and evaporation is the only real cooling system your body has. So 35 degrees at 65 percent humidity in Karachi feels closer to 47, while 40 degrees at 25 percent humidity in Dubai feels like 39. Same body, very different days. This calculator uses the NOAA formula your local weather service quietly uses too, then pairs it with live readings from open-meteo so you can compare what the forecast claims with what your skin already knew. Use it to decide whether the kids' cricket session is happening today, whether your evening run should move indoors, or whether your elderly parent needs you to drop by with cold water. Numbers don't replace common sense — but they do help you trust your gut instead of overriding it.

Pro tips most people learn the hard way

The Rothfusz formula assumes shade. If you're in direct sunlight, add 5 to 10 degrees to the displayed heat index for a realistic feel — which is why noon-to-3 PM outdoor work in Pakistani summers crosses into genuinely dangerous territory even when the forecast looks routine.
Watch the wet-bulb temperature, not the heat index, for true survival thresholds. A wet-bulb above 35 degrees C is the limit beyond which a healthy human cannot cool themselves no matter what — and parts of Jacobabad and the Gulf cross this for hours every summer.
Heat exhaustion sneaks up on people who think they're tough. Early signs: headache, dizziness, nausea, stopped sweating. If sweating stops in real heat, you're in heatstroke territory — get to shade, water, and a cold compress immediately and call for help.
Indoor isn't automatically safer. A flat above 30 degrees with 80 percent humidity and no AC produces a heat index near 38 — the same risk band as outdoor mid-day. Cross-ventilation, a wet cloth on the neck, and ORS sachets matter for the elderly and infants especially.
Different countries use different 'feels like' formulas — AccuWeather RealFeel, Canada's Humidex, Australia's Apparent Temperature — and they disagree by 2 to 3 degrees in extreme heat. This calculator uses the NOAA standard, which is what the US National Weather Service and most international heat-warning systems align to.

?What is the Heat Index Calculator?

The Heat Index — also called 'apparent temperature' or simply 'feels like' temperature — combines air temperature and relative humidity into a single number that better reflects how hot the body actually perceives the conditions. When humidity is high, sweat evaporates more slowly, so the body cannot cool itself as effectively. Two days at the same air temperature can feel completely different depending on humidity. This calculator uses the NOAA Rothfusz regression formula and live weather data from open-meteo.com so you can compare the air temperature reported by your forecast with what your body actually experiences.

The Formula

HI (°F) = c₁ + c₂T + c₃R + c₄TR + c₅T² + c₆R² + c₇T²R + c₈TR² + c₉T²R², where T is air temperature in °F and R is relative humidity in %.

The Rothfusz regression is the polynomial used by the U.S. National Weather Service. It is valid for T ≥ 80 °F (≈ 27 °C) and R ≥ 40%. Below those thresholds the calculator falls back to a simpler Steadman approximation. NOAA also applies small corrections for very low humidity (RH < 13%) and very high humidity (RH > 85%) within specific temperature ranges. The output category — Caution, Extreme Caution, Danger, Extreme Danger — follows NOAA thresholds and aligns with widely published heat-safety guidance.

Heat Index Reference — Air Temperature × Humidity → 'Feels Like'

How the same air temperature feels at different humidity levels (NOAA Rothfusz regression). All values in °C.

Air Temp	30% RH	50% RH	70% RH	90% RH
27 °C / 80 °F	26 °C	27 °C	29 °C	31 °C
29 °C / 84 °F	28 °C	30 °C	32 °C	35 °C
32 °C / 90 °F	31 °C	34 °C	38 °C	44 °C
35 °C / 95 °F	34 °C	39 °C	47 °C	57 °C
38 °C / 100 °F	38 °C	44 °C	57 °C	—
40 °C / 104 °F	41 °C	51 °C	—	—
43 °C / 110 °F	45 °C	59 °C	—	—

Put It in Perspective

32 °C with 70% humidity (typical Karachi summer afternoon) feels like 38 °C — entering NOAA's 'Extreme Caution' band.

35 °C with 60% humidity in Lahore feels like 45 °C — beyond what most outdoor workers can sustain safely without breaks.

Dubai at 40 °C with low 25% humidity feels like only ~39 °C — dry desert heat is more tolerable than humid coastal heat at the same thermometer reading.

27 °C and 50% humidity is roughly room-comfort indoors — the heat-index formula barely moves above the air temp here.

A wet-bulb temperature of 35 °C (the survivability limit) corresponds to a heat index near 60 °C — beyond every NOAA category.

Saunas operate at 80–90 °C with very low humidity — the dry heat is tolerable; add steam (Turkish hammam) and the apparent heat skyrockets.

Practical Examples

32 °C (90 °F) air at 70% humidity feels like ≈ 41 °C (106 °F) — entering the 'Danger' band even though the thermometer hasn't crossed 35 °C.

40 °C (104 °F) air at 30% humidity feels like ≈ 39 °C — still extreme, but dry heat is more tolerable than the same number with moisture.

Karachi summer afternoons (35 °C, 65% RH) routinely produce a heat index above 47 °C, which explains why the city issues heatwave alerts even when the air temperature is 'only' 35–37 °C.

Indoor environments above 30 °C with 80%+ humidity (no AC, no fan) can produce heat-index readings near 38 °C — long enough exposure causes heat exhaustion in healthy adults.

Frequently Asked Questions

Your body cools itself almost entirely by sweating — and sweat only cools you when it evaporates. When the air is already saturated with moisture, sweat just sits on your skin without evaporating, so your internal temperature keeps climbing while your shirt gets wet. That's why a humid 32 degrees in Karachi feels far worse than a dry 38 in Dubai. Same thermometer reading; completely different physiology.

Popular Conversions

Jump to a ready-made conversion — useful for quick reference and sharing:

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Heat Index Calculator

Health

Find the 'feels like' temperature from air temperature and humidity. Live weather for your country.

Health

Heat Index Calculator

Generated on May 23, 2026

Loading current weather…

Air Temperature

Relative Humidity

Save / share— download or share to WhatsApp, Facebook & more

Premium Converters

Heat Index Result

Feels like 37°C / 99°F — Extreme Caution

Generated

5/23/2026

Feels Like (Heat Index)

37°C

99 °F

Extreme Caution

Air: 32°C · 89.6°F · 60% RH

Heat cramps and heat exhaustion possible. Limit strenuous outdoor activity, especially midday.

Why does humidity make it feel hotter?

Heat-index estimates are based on shaded conditions and a light wind. Direct sun, calm air, or strenuous activity can push the felt temperature 5–10 °C higher.

Step-by-step calculation

Formula

HI ≈ Rothfusz regression (NOAA): HI = c₁ + c₂T + c₃R + c₄TR + c₅T² + c₆R² + c₇T²R + c₈TR² + c₉T²R²

1Temperature = 32°C = 89.6°F
2Relative humidity = 60%
3Within the Rothfusz regression's valid range — applying full NOAA polynomial.
4Heat Index = 98.7°F = 37.1°C → Extreme Caution

Quick Answer

Find the 'feels like' temperature from air temperature and humidity. Live weather for your country.

Overview — Heat Index Calculator

Health

Formula

HI (°F) = c₁ + c₂T + c₃R + c₄TR + c₅T² + c₆R² + c₇T²R + c₈TR² + c₉T²R²,  where T is air temperature in °F and R is relative humidity in %.

32 °C with 70% humidity (typical Karachi summer afternoon) feels like 38 °C — entering NOAA's 'Extreme Caution' band.

35 °C with 60% humidity in Lahore feels like 45 °C — beyond what most outdoor workers can sustain safely without breaks.

Dubai at 40 °C with low 25% humidity feels like only ~39 °C — dry desert heat is more tolerable than humid coastal heat at the same thermometer reading.

By Muhammad Salman SaleemUpdated: May 23, 2026MethodologyFree, no sign-upRuns in your browser — your data stays private

From the editors — what to know before you start

Pro tips most people learn the hard way

The Rothfusz formula assumes shade. If you're in direct sunlight, add 5 to 10 degrees to the displayed heat index for a realistic feel — which is why noon-to-3 PM outdoor work in Pakistani summers crosses into genuinely dangerous territory even when the forecast looks routine.
Watch the wet-bulb temperature, not the heat index, for true survival thresholds. A wet-bulb above 35 degrees C is the limit beyond which a healthy human cannot cool themselves no matter what — and parts of Jacobabad and the Gulf cross this for hours every summer.
Heat exhaustion sneaks up on people who think they're tough. Early signs: headache, dizziness, nausea, stopped sweating. If sweating stops in real heat, you're in heatstroke territory — get to shade, water, and a cold compress immediately and call for help.
Indoor isn't automatically safer. A flat above 30 degrees with 80 percent humidity and no AC produces a heat index near 38 — the same risk band as outdoor mid-day. Cross-ventilation, a wet cloth on the neck, and ORS sachets matter for the elderly and infants especially.
Different countries use different 'feels like' formulas — AccuWeather RealFeel, Canada's Humidex, Australia's Apparent Temperature — and they disagree by 2 to 3 degrees in extreme heat. This calculator uses the NOAA standard, which is what the US National Weather Service and most international heat-warning systems align to.

?What is the Heat Index Calculator?

The Formula

HI (°F) = c₁ + c₂T + c₃R + c₄TR + c₅T² + c₆R² + c₇T²R + c₈TR² + c₉T²R², where T is air temperature in °F and R is relative humidity in %.

Heat Index Reference — Air Temperature × Humidity → 'Feels Like'

How the same air temperature feels at different humidity levels (NOAA Rothfusz regression). All values in °C.

Air Temp	30% RH	50% RH	70% RH	90% RH
27 °C / 80 °F	26 °C	27 °C	29 °C	31 °C
29 °C / 84 °F	28 °C	30 °C	32 °C	35 °C
32 °C / 90 °F	31 °C	34 °C	38 °C	44 °C
35 °C / 95 °F	34 °C	39 °C	47 °C	57 °C
38 °C / 100 °F	38 °C	44 °C	57 °C	—
40 °C / 104 °F	41 °C	51 °C	—	—
43 °C / 110 °F	45 °C	59 °C	—	—

Put It in Perspective

32 °C with 70% humidity (typical Karachi summer afternoon) feels like 38 °C — entering NOAA's 'Extreme Caution' band.

35 °C with 60% humidity in Lahore feels like 45 °C — beyond what most outdoor workers can sustain safely without breaks.

Dubai at 40 °C with low 25% humidity feels like only ~39 °C — dry desert heat is more tolerable than humid coastal heat at the same thermometer reading.

27 °C and 50% humidity is roughly room-comfort indoors — the heat-index formula barely moves above the air temp here.

A wet-bulb temperature of 35 °C (the survivability limit) corresponds to a heat index near 60 °C — beyond every NOAA category.

Saunas operate at 80–90 °C with very low humidity — the dry heat is tolerable; add steam (Turkish hammam) and the apparent heat skyrockets.

Practical Examples

32 °C (90 °F) air at 70% humidity feels like ≈ 41 °C (106 °F) — entering the 'Danger' band even though the thermometer hasn't crossed 35 °C.

40 °C (104 °F) air at 30% humidity feels like ≈ 39 °C — still extreme, but dry heat is more tolerable than the same number with moisture.

Karachi summer afternoons (35 °C, 65% RH) routinely produce a heat index above 47 °C, which explains why the city issues heatwave alerts even when the air temperature is 'only' 35–37 °C.

Indoor environments above 30 °C with 80%+ humidity (no AC, no fan) can produce heat-index readings near 38 °C — long enough exposure causes heat exhaustion in healthy adults.

Frequently Asked Questions

Popular Conversions

Jump to a ready-made conversion — useful for quick reference and sharing:

Browse all Health

BMI Calculator

Calculate Body Mass Index against WHO and Asian-population thresholds for men and women using kg or lb, cm or inches, with healthy-range guidance.

BMR Calculator

Estimate Basal Metabolic Rate using the Mifflin-St Jeor equation by sex, age, weight and height — the resting kcal/day baseline for diet planning.

TDEE Calculator

Compute Total Daily Energy Expenditure from BMR and activity multiplier (sedentary to extra active) to set kcal targets for cutting, maintenance, or bulking.

Ideal Weight Calculator

Find your ideal weight range in kg and lb using the Robinson, Miller, Devine and Hamwi formulas alongside the BMI 18.5-24.9 healthy band for men and women.

Water Intake Calculator

Calculate daily water intake in millilitres or litres from body weight and exercise minutes, with hot-climate, pregnancy and breastfeeding adjustments.

Body Fat Calculator

Estimate body fat percentage with the US Navy tape-measure method using neck, waist and hip in cm or inches — a no-cost alternative to DEXA scans for men and women.

Macro Calculator

Calculate your daily protein, carbohydrate, and fat targets based on your goals.

Pregnancy Due Date Calculator

Estimate baby's due date using Naegele's rule (LMP + 280 days), adjusted for cycle length, with conception date, trimester boundaries and current week and day.

Browse all Health calculators & converters

See every tool in this category, plus FAQs and category-specific guides.

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Heat Index Calculator — the 'feels like' temperature from air temperature and… | Premium Converters

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Heat Index Calculator

Heat Index Calculator

Heat Index Result

Step-by-step calculation

Overview — Heat Index Calculator

From the editors — what to know before you start

Pro tips most people learn the hard way

?What is the Heat Index Calculator?

The Formula

Heat Index Reference — Air Temperature × Humidity → 'Feels Like'

Put It in Perspective

Practical Examples

Frequently Asked Questions

Popular Conversions

Embed this calculator on your site

Browse other categories

Premium Converters

Heat Index Calculator

Heat Index Calculator

Heat Index Result

Step-by-step calculation

Overview — Heat Index Calculator

From the editors — what to know before you start

Pro tips most people learn the hard way

?What is the Heat Index Calculator?

The Formula

Heat Index Reference — Air Temperature × Humidity → 'Feels Like'

Put It in Perspective

Practical Examples

Frequently Asked Questions

Popular Conversions

Embed this calculator on your site

Browse other categories

Premium Converters

Premium Converters

Heat Index Calculator

Heat Index Calculator

Step-by-step calculation

Overview — Heat Index Calculator

From the editors — what to know before you start

Pro tips most people learn the hard way

?What is the Heat Index Calculator?

The Formula

Heat Index Reference — Air Temperature × Humidity → 'Feels Like'

Put It in Perspective

Practical Examples

Frequently Asked Questions

Why does humidity make hot weather worse?

Is heat index the same as 'real-feel' temperature?

Above what heat index is it dangerous to exercise outdoors?

Does this account for direct sunlight?

What's the difference between heat index and wet-bulb temperature?

Why does my country's forecast app show a different number?

Popular Conversions

Embed this calculator on your site

More Health Tools

Browse other categories

Premium Converters

Heat Index Calculator

Heat Index Calculator

Step-by-step calculation

Overview — Heat Index Calculator

From the editors — what to know before you start

Pro tips most people learn the hard way

?What is the Heat Index Calculator?

The Formula

Heat Index Reference — Air Temperature × Humidity → 'Feels Like'

Put It in Perspective

Practical Examples

Frequently Asked Questions

Why does humidity make hot weather worse?

Is heat index the same as 'real-feel' temperature?

Above what heat index is it dangerous to exercise outdoors?

Does this account for direct sunlight?

What's the difference between heat index and wet-bulb temperature?

Why does my country's forecast app show a different number?

Popular Conversions

Embed this calculator on your site

More Health Tools

Browse other categories