Calculate water cooling wattage from coolant flow rate and temperature rise, or find the flow or temperature change needed for a heat load in W or BTU/h.

Assumes a steady liquid stream with constant properties. It does not size a radiator.

Water uses 1000 kg/mยณ and 4182 J/(kgยทK). Glycol options are typical values; choose Custom to enter your coolant’s data.

A temperature difference has no 32-degree offset.

Optional settings

Related Calculators

Water Cooling Wattage Formula

The steady-flow sensible-heat model is Qฬ‡ = แน cp |ฮ”T| = ฯ Vฬ‡ cp |ฮ”T|. With volumetric flow F in L/min, water density 1000 kg/mยณ and cp = 4182 J/(kgยทK), the coefficient is 69.7 W per (L/minยทK).

Qฬ‡ = 69.7 ร— F ร— |ฮ”T|
F = Qฬ‡ รท (69.7 ร— |ฮ”T|)
|ฮ”T| = Qฬ‡ รท (69.7 ร— F)
  • Qฬ‡ = sensible heat-transfer rate magnitude, in watts
  • F = water flow rate, in liters per minute
  • ฮ”T = temperature difference between inlet and outlet water, in ยฐC
  • 69.7 = coefficient for this constant-property water approximation

The water preset uses 4182 J/(kgยทK) and 1000 kg/mยณ as approximations. PG30 and PG50 preserve the prior 1030/3700 and 1060/3400 density/specific-heat pairs as illustrative scenarios; their temperature and mass/volume concentration basis were unspecified, so they are not verified mixture data. For a real coolant, enter manufacturer properties at the stated concentration basis and operating or mean temperature. A 1ยฐF difference equals 5/9 K; absolute Fahrenheit temperatures also require the 32-degree offset.

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 US GPM = 3.785411784 L/min Convert gallons per minute to liters per minute
Temperature difference 1ยฐF difference = 5/9ยฐC difference Convert a Fahrenheit temperature rise or drop

Cooling Wattage per 1 L/min of Water Flow

Quick checks for the same 1000 kg/mยณ, 4182 J/(kgยทK) water approximation. Values scale linearly with flow and temperature difference while properties remain constant.

Water ฮ”T Cooling at 1 L/min Cooling at 1 L/min
1ยฐC 69.7 W 237.8 BtuIT/h
2ยฐC 139.4 W 475.7 BtuIT/h
5ยฐC 348.5 W 1,189.1 BtuIT/h
10ยฐC 697.0 W 2,378.3 BtuIT/h

Example Check

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

Qฬ‡ = 69.7 ร— 3 ร— 4 = 836.4 W

At constant properties, a larger temperature difference or flow increases the sensible heat carried by the stream. Mass-flow modes use Qฬ‡ = แน cp |Tenter โˆ’ Tleave| and can reverse for mass flow. Cooling uses Tleave = Tenter โˆ’ Qฬ‡/(แน cp); heating uses the plus sign, and the entering-temperature mode reverses it. The model assumes steady single-phase liquid flow with suitable mean properties. It excludes latent heat, pump heat, fouling and heat-exchanger approach; it does not establish radiator capacity. Check freezing/boiling limits and actual equipment performance separately.