Behind-the-Meter Power Sizer
Turn an IT load into facility megawatts, generator count with redundancy, and daily gas burn.
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How to Use It
Enter the IT load you plan to serve and a design PUE to get the total facility load. Pick a generator unit size and a redundancy level to see how many units run and how many you install. The heat rate turns that load into daily gas burn.
How This Calculator Works
The calculator runs these formulas in your browser:
- Facility load (MW) = IT load (MW) × design PUE
- Units running = facility load ÷ unit size, rounded up
- Units installed = units running + 1 (N+1) or + 2 (N+2), or units running × 2 (2N)
- Gas burn (MMBtu/day) = facility load (kW) × heat rate (Btu/kWh) × 24 ÷ 1,000,000
- Gas volume (Mcf/day) = MMBtu/day ÷ 1.036 (1,036 Btu per cubic foot)
- Energy per year (MWh) = facility load (MW) × 8,760 hours
Default assumptions and sources
The 1,036 Btu per cubic foot conversion is the typical U.S. heat content in the EIA energy units page. Heat rates for real fleets are in the EIA Electric Power Annual, Table 8.2: in 2024, gas-fired internal combustion engines averaged about 8,900 Btu/kWh and simple-cycle gas turbines about 11,000.
Worked example
With the defaults, 100 MW of IT load at a design PUE of 1.25 needs 125 MW at the facility. With 4.5 MW units, 125 ÷ 4.5 = 27.8, so 28 units run; N+1 means 29 installed, or 130.5 MW of nameplate. At 8,500 Btu/kWh the plant burns 125,000 × 8,500 × 24 ÷ 1,000,000 = 25,500 MMBtu a day, about 24.6 MMcf, and makes about 1,095,000 MWh a year at full load.
Limits
It assumes every unit runs at full rated output, at one heat rate, all day. Real plants derate for altitude and heat, run below full load, add parasitic loads (cooling fans, gas compression) and plan maintenance outages, so treat the answer as a first sketch for talking to vendors.
Common Questions
What is a good design PUE for an off-grid site?
New air-cooled and liquid-cooled sites are often designed somewhere around 1.2 to 1.4. Hot, dry climates and older designs run higher. Use your cooling designer's number when you have one.
Why does redundancy matter more off-grid?
With no utility to fall back on, a tripped or maintained unit must be covered by a spare. N+1 covers one unit out; N+2 covers a unit in maintenance plus a trip; 2N doubles everything.
Is the gas number exact?
No. It assumes full load all day at one heat rate. Part-load operation, ambient temperature, altitude and parasitic loads all change real fuel use.