What formula does this calculator use?

It uses the NWS (US National Weather Service) and Environment and Climate Change Canada wind chill index formula adopted in 2001 — WC = 13.12 + 0.6215·T − 11.37·V^0.16 + 0.3965·T·V^0.16 — where T is the air temperature in °C and V is the wind speed in km/h. This replaced the older Siple-Passel formula and was validated against skin-temperature measurements taken at Windsor, Ontario.

Why does wind make it feel colder than the thermometer says?

Moving air carries heat away from exposed skin faster than still air does. The faster the wind, the faster the top layer of warm air next to your skin is stripped away and replaced by cold air. The wind chill index quantifies that effect as an equivalent still-air temperature — the temperature at which the same rate of heat loss would occur with no wind.

What are the frostbite risk levels?

The five levels are Low (no significant risk), Moderate (exposed skin may freeze in 10–30 min), High (5–10 min), Very High (2–5 min), and Extreme (under 2 min). These thresholds are published by Environment and Climate Change Canada and the NWS. They assume light activity and standard clothing; wet clothing, poor circulation, or higher altitude raises the risk.

Does the formula work for temperatures above 10 °C?

No. The NWS formula is only defined for air temperatures at or below 10 °C (50 °F) and wind speeds of at least 3 km/h (1.9 mph). When either condition is not met, the wind chill equals the actual temperature and the calculator notes that the formula is out of range.

How do I convert my result between Celsius and Fahrenheit?

Use the °C / °F toggle at the top of the calculator — it converts both the inputs and the output simultaneously so you never need to do unit arithmetic yourself. For reference, 0 °C = 32 °F, −10 °C = 14 °F, −20 °C = −4 °F, and −40 °C = −40 °F (the point where the scales cross).

Is wind chill the same as the heat index?

No. Wind chill measures the cooling effect of wind on exposed skin in cold conditions. The heat index (or "feels like" in summer) measures the combined effect of heat and humidity — high humidity slows evaporation of sweat, making hot days feel even hotter. Both are apparent-temperature indices but they apply to opposite ends of the thermometer.

Wind Chill Calculator

On a cold winter morning the thermometer might read −8 °C, but if a 30 km/h wind is blowing it can feel closer to −16 °C. That gap between the measured temperature and what your body actually experiences is the wind chill — and knowing it matters for dressing correctly, managing outdoor work, and protecting children and the elderly from frostbite.

This calculator implements the official NWS / Environment Canada 2001 formula, works in both Celsius/Fahrenheit and km/h/mph, and pairs every result with a colour-coded frostbite risk rating backed by the same thresholds used on Canadian weather forecasts.

How it works

Wind chill is calculated from two measurements:

T — the air temperature in °C (dry-bulb, standard meteorological thermometer)
V — the wind speed in km/h at the standard 10-metre reference height

The NWS formula is:

WC = 13.12 + 0.6215 · T − 11.37 · V^0.16 + 0.3965 · T · V^0.16

The exponent 0.16 captures the non-linear relationship between wind speed and heat transfer: doubling the wind does not double the cooling effect, but it still meaningfully increases it. The formula was calibrated using volunteer subjects in a wind tunnel and validated with skin-temperature sensors in real outdoor conditions at Windsor, Ontario.

Valid range: T ≤ 10 °C and V ≥ 3 km/h. Below 3 km/h the air movement is so slight that wind chill equals the actual temperature. Above 10 °C wind speeds cool the body but the mechanism differs (evaporative cooling dominates), so a separate formula applies there.

The frostbite risk thresholds — Low, Moderate, High, Very High, Extreme — map directly onto the wind chill temperature and indicate how quickly exposed facial skin can freeze. They assume someone is dressed for the temperature but not wearing a full face mask.

Worked example

Suppose it is −12 °C with a 40 km/h wind:

V^0.16 = 40^0.16 ≈ 1.9953
WC = 13.12 + 0.6215 × (−12) − 11.37 × 1.9953 + 0.3965 × (−12) × 1.9953
WC = 13.12 − 7.458 − 22.687 − 9.495
WC ≈ −26.5 °C

That is a High frostbite risk: exposed skin such as cheeks, nose, or ears can freeze in as little as 5–10 minutes without protection. A face covering and warm gloves are essential.

Air temp	Wind	Wind chill	Risk
−5 °C	20 km/h	−11 °C	Moderate
−10 °C	30 km/h	−20 °C	High
−20 °C	50 km/h	−36 °C	Very High
−35 °C	60 km/h	−56 °C	Extreme

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