Factorio steam power calculator

How to use the result

Read the demand from the electric network you want to support. Enter that demand in megawatts (MW). If your figure is in kilowatts, divide it by 1,000 first: 900 kW is 0.9 MW.

The capacity margin adds planned spare generation above the demand you entered. For example, 20% on a 9 MW factory asks the calculator to provide at least 10.8 MW. It is a sizing choice, not a forecast of how fast your factory will grow.

Build the result as a connected system with enough water and fuel. The displayed capacity is an upper bound for the engine bank, not a guarantee of delivered power under interrupted inputs.

The formula

Target MW = demand MW × (1 + capacity margin / 100)
Steam engines = round up(target MW / 0.9)
Boilers = round up(steam engines / 2)
Installed capacity MW = steam engines × 0.9

Engines are rounded up first because a fraction of an engine cannot be built. Boilers are then rounded up so that every engine has enough potential steam supply.

If the engine count is odd, the last boiler has unused steam-production capacity at full load. The calculator keeps that valid odd count rather than adding an engine you did not ask for. You can add another engine later if you need the extra capacity.

A worked example

With 9 MW demand and 20% margin, the target is 10.8 MW. Twelve engines provide exactly 10.8 MW, supported by six boilers.

With 1 MW demand and 0% margin, one engine would be too small. The result rounds to two engines and one boiler, for 1.8 MW of installed capacity. The 0.8 MW above the target comes from whole-machine rounding.

What this tool leaves out

The tool does not size fuel mining, belts, inserters, offshore pumps, pipe networks, steam storage or backup generation. It does not model time-varying consumption, other quality levels, modded statistics or nuclear power.

Inputs accept demand above zero through 100,000 MW, and a capacity margin from 0 to 200%. Those are practical input bounds for this tool, not game limits. When an input is invalid, the previous result is hidden so it cannot be mistaken for a current calculation.

For the underlying machine statistics, read the steam power ratio guide. If a correctly sized bank still does not work, follow the power troubleshooting checks.