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Gas Turbine Output Calculator

Work out gas turbine output instantly with clear inputs, formula shown and shareable results.

About Gas Turbine Output Calculator

Gas turbine output is quoted at ISO conditions of 15 C at sea level. Real output falls roughly 0.7% per degree above 15 C because hot air is less dense and the compressor moves less mass, and further with altitude as ambient pressure drops. Inlet filters and exhaust ducting take another 1-3%.

Formulas

Temperature derate

Factor = 1 - 0.007 x (ambient T - 15)

Altitude derate

Factor = (1 - 2.25577e-5 x altitude)^5.2559

Worked example

With the default values below, Gas Turbine Output Calculator returns Site-Rated Output of 142.811. Change any input above and every figure here is recalculated in your browser.

Inputs used

ISO Rated Outputminimum 0 MW
180 MW
Ambient Temperatureminimum -50 degrees C
38 degrees C
Site Altitudeminimum 0 m
300 m
Inlet And Exhaust Pressure Loss Derateaccepts 0–15 %
2 %

Results

Site-Rated Output
142.811
Temperature Derate Factor
0.83900
Altitude Derate Factor
0.96494
Output Lost Against ISO Rating
37.189

Step by step

  1. 1Values used
  2. 2Temperature derate
  3. 3Altitude derate
  4. 4Site-Rated Output= 142.811
  5. 5Temperature Derate Factor= 0.83900
  6. 6Altitude Derate Factor= 0.96494
  7. 7Output Lost Against ISO Rating= 37.189

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 5 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 hot weather hurt gas turbines most?

They are constant-volume machines, so mass flow falls directly with air density. A 40 C day can cost 15-20% of ISO output — exactly when electricity demand peaks.

What can recover the lost output?

Inlet air cooling — evaporative coolers, fogging or mechanical chillers — restores much of the temperature derate and is standard in hot climates.

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Gas Turbine Output Calculator – Calculate Site-Rated Output