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Heat index calculator

Find the 'feels-like' temperature in hot, humid weather.

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The Heat index calculator turns Temperature (°C), Relative humidity (%) into Feels like (°C), instantly and for free. For instance, with Temperature (°C) = 32 and Relative humidity (%) = 70 it returns Feels like (°C) = 40.409.

How to use it

  1. Enter your values: Temperature (°C), Relative humidity (%).
  2. Read the result instantly: Feels like (°C).

Frequently asked questions

How does the Heat index calculator work?

It takes Temperature (°C) and Relative humidity (%) and derives Feels like (°C) from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

2 values: Temperature (°C) and Relative humidity (%). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Temperature (°C) = 32 and Relative humidity (%) = 70, the calculator returns Feels like (°C) = 40.409. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Temperature (°C) = 35 and Relative humidity (%) = 140 instead, Feels like (°C) goes from 40.409 to 113.012 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Temperature (°C) = 29 and Relative humidity (%) = 35, Feels like (°C) comes out at 28.2. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Putting a number on what something costs or feels like: an appliance's share of the bill, a flight's emissions, a household's footprint, or how cold the wind actually makes it.

What is the most common mistake?

Reading a nameplate rating as an average. A 2000 W appliance draws that at full load, not continuously — a fridge rated at 150 W runs a fraction of the hour, so its yearly cost is nowhere near 150 W times 8760.

What is the difference between the Heat index calculator and the Wind chill calculator?

Both return Feels like (°C). What differs is what they ask for: this one wants Relative humidity (%), the Wind chill calculator wants Wind speed (km/h). Use whichever matches the numbers you already have.

Where do the figures come from, and how current are they?

The arithmetic is exact for the rating and tariff you enter. Emission factors come from published national inventories and differ by a factor of several between electricity grids, so a footprint is only as local as the factor behind it.

Further reading

All guides →
ExplainerWhat Is the Heat Index? Why It Feels Hotter Than It IsThe heat index combines air temperature and humidity into a single 'feels-like' number, and explains why a humid 90-degree day can be dangerous.ExplainerWind Chill: What the “Feels Like” Number Actually MeasuresThe calculator runs the 2001 index, not the 1945 one, and refuses to answer above 50 °F or under 3 mph. Here is what its number is a model of — bare skin, in shade, walking — and the two things it says nothing about: a clothed body, and a parked car.ExplainerHow Much Electricity Do Appliances Use? Watts, kWh and CostHow watts turn into kilowatt-hours, what typical appliances draw, and how to translate that consumption into a cost on your bill.ExplainerDew Point: What It Is, and How the Calculator Gets ItMagnus–Tetens with the Alduchov–Eskridge coefficients, 17.625 and 243.04. Why an absolute number beats relative humidity for judging comfort, what temperature a window has to reach before it runs, and the one input the calculator does not check.How-toHow Much Does an Appliance Cost to Run? A Simple MethodTurn an appliance's wattage and daily hours into an annual running cost using one formula: power times hours times your price per kWh.ExplainerWhere Household Water Actually GoesPeople picture taps and showers, and metered end-use studies say the biggest single line is somewhere else. Here is the ranked budget from named national agencies, plus the arithmetic that changes behaviour: the dripping tap, the running tap, and the shower flow rate at which a bath becomes the cheaper option.