Generator Size Calculator

Starting surge is what kills undersized generators

A fridge compressor draws three to five times its running wattage for a second or two at start-up. A 700 W fridge can demand 2,200 W at that instant. Size for the running total plus the single largest surge — not the sum of all surges, since motors rarely start simultaneously.

What this page needs from you

This page asks for total running watts in W, largest starting surge in W and safety margin as a percentage. From those it returns generator size needed in W, together with in kilowatts, running load only, fuel at 0.4 l per kwh and amps at 230 v. Every figure updates as you type, and nothing you enter leaves your browser.

Running short costs more than over-ordering

A second delivery carries its own charge, materials from a different batch may not match, and a job halted halfway often has to be redone at the join. Ordering slightly long is cheap insurance against all three.

Measure twice, and allow for waste

A 5% error on one dimension becomes 10% on an area and 15% on a volume, which is why checking the tape matters more than the arithmetic. On top of the measured quantity, allow the trade standard of 10% for cuts and breakage, and 15 to 20% for diagonal layouts, complex shapes or anything cut around obstacles.