Calculate water cooling wattage, flow rate, or temperature difference from any two inputs, with W or BTU/hr, L/min or GPM, and °C or °F.

Water Cooling Wattage Calculator

Enter any 2 values to calculate the missing variable

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Water Cooling Wattage Formula

In base units, the calculator uses water heat transfer with flow in L/min and temperature difference in °C.

Q = 69.7333 \times F \times \Delta T
F = \frac{Q}{69.7333 \times \Delta T}
\Delta T = \frac{Q}{69.7333 \times F}
  • Q = cooling wattage, in watts
  • F = water flow rate, in liters per minute
  • ΔT = temperature difference between inlet and outlet water, in °C
  • 69.7333 = water heat transfer factor based on water specific heat and density

The factor assumes liquid water with a specific heat of about 4184 J/kg·°C and a density of about 1 kg/L. Temperature difference in °F is converted as 1°F difference = 5/9°C difference. Results will change if you use glycol mixtures or another coolant.

Water Cooling Unit Conversions

These are the conversions used before and after the main calculation.

Quantity Conversion Use
Power 1 W = 3.41214 BTU/hr Convert watts to BTU/hr
Power 1 BTU/hr = 0.293071 W Convert BTU/hr to watts
Flow rate 1 GPM = 3.78541 L/min Convert gallons per minute to liters per minute
Temperature difference 1°F difference = 5/9°C difference Convert a Fahrenheit temperature rise or drop

Cooling Wattage per 1 L/min of Water Flow

Use this table as a quick check. Values scale linearly with flow rate.

Water ΔT Cooling at 1 L/min Cooling at 1 L/min
1°C 69.7 W 237.9 BTU/hr
2°C 139.5 W 475.8 BTU/hr
5°C 348.7 W 1,189.8 BTU/hr
10°C 697.3 W 2,379.7 BTU/hr

Example Check

If water flows at 3 L/min and rises by 4°C, the cooling wattage is:

Q = 69.7333 \times 3 \times 4 = 836.8 W

A larger temperature difference means each liter of water carries away more heat. A larger flow rate means more water is carrying heat away each minute.