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Radiator Capacity Calculator

Work out radiator capacity instantly with clear inputs, formula shown and shareable results.

About Radiator Capacity Calculator

About a third of fuel energy leaves through the coolant. Flow follows from Q = m cp deltaT with a 50/50 glycol mix at about 3.6 kJ/kg·K, and the airflow needed depends on the temperature difference between coolant and ambient — which is why cooling is marginal on hot days.

Formula

Cooling load

heat = power x rejection fraction; flow = heat / (cp x deltaT); airflow = heat / (rho cp deltaT_air)

Worked example

With the default values below, Radiator Capacity Calculator returns Heat to reject of 45.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Engine power
150 kW
Heat to coolant
30 %
Coolant temperature drop
8 °C
Ambient temperature
35 °C

Results

Heat to reject
45.00 kW
Coolant flow required
93.75 L/min
Airflow required
40.71 m³/min
Approximate core area
0.82 m²

Step by step

  1. 1Values used
  2. 2Cooling load
  3. 3Heat to reject= 45.00 kW
  4. 4Coolant flow required= 93.75 L/min
  5. 5Airflow required= 40.71 m³/min
  6. 6Approximate core area= 0.82 m²

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does cooling fail in traffic?

Airflow through the core depends on road speed or the fan. Stationary, only the fan provides it, and at high ambient the temperature difference is small.

Does a bigger radiator always help?

Only if airflow is available. Core thickness beyond about 40 mm gives diminishing returns because the air heats up passing through the first rows.

Related Calculators

Radiator Capacity Calculator – Calculate Heat to reject