Power Tool Generator Size Calculator

Data reviewed 2026-07-05 ·how we calculate

Job-site generator sizing has one rule: size for the biggest motor you own, because tool motors start dozens of times an hour and every trigger pull is a fresh surge. A 7-1/4 inch circular saw that cuts at 1,400W spikes to roughly 2,300W at trigger pull; a 10-inch table saw nearly doubles that. Pick your dominant tool below — the calculator handles the surge math, and the FAQ covers the modern alternative that is quietly ending this problem: battery platforms charged from a much smaller generator.

Size a generator for this load

Computed on typical values; ranges shown below. 25% headroom applied.

Generator safety — read every time

Never run a generator indoors, in a garage, or near windows, doors or vents.Carbon monoxide kills quickly and without warning — place the generator 20+ feet from the house with the exhaust pointed away, and use battery CO detectors inside.
Never backfeed your house through a wall outlet or dryer outlet. Backfeeding can electrocute utility line workers and destroy equipment when power returns.
Connecting a generator to home circuits requires a transfer switch or interlock installed by a licensed electrician. There is no safe DIY shortcut, and this site does not provide wiring instructions.
Use heavy, outdoor-rated extension cords (12-gauge or thicker), fully uncoiled, sized to the load and the distance.

How to size it step by step

Identify the biggest motor that will run on the generator — not the average tool, the worst one. Its trigger surge sets the requirement; smaller tools ride along free.
Add anything running simultaneously: a shop vac (800–1,100W) alongside the saw, work lights, a battery charger bank. Sum running watts, then add only the big tool’s surge delta.
Apply 25% headroom: a circular-saw site wants 2,300W × 1.25 = 2,875W → the 3,500–4,500W class. A table-saw or miter-saw site wants 5,000W with the same math.
GFCI everything: OSHA requires ground-fault protection for construction receptacle use — many jobsite generators have GFCI outlets built in; otherwise use a GFCI pigtail at the generator, and heavy 12/10-gauge cords sized to the run.

Pro tips

Check your nameplate first — every figure on this page is a planning estimate, and the label on your specific unit beats any chart.
Uncoil cords fully under load — a coiled cord carrying 15A is a heater wrapped in itself, and site cords die exactly that way.
Log the generator’s hours and change oil per the manual (often every 50–100 hours) — jobsite duty accumulates hours far faster than storm duty, and small engines forgive nothing.

The data behind this calculator

Common corded tool loads (running / trigger surge)
Figure	Value	Source
Drill, 1/2 in corded	~600W / ~900W	DeWalt/Milwaukee nameplates; sizing charts
Circular saw, 7-1/4 in	~1,400W / ~2,300W	DeWalt/Makita nameplates; sizing charts
Miter saw, 10–12 in	~1,800W / ~3,600W	DeWalt/Bosch nameplates; sizing charts
Table saw, 10 in jobsite	~2,000W / ~4,000W	DeWalt/SawStop nameplates; sizing charts
Battery charger (alternative path)	~100–300W per charger, no surge	DeWalt/Milwaukee rapid charger specifications

Duty cycle: Tools start and stop constantly — a trim carpenter’s miter saw may surge 200 times a day. The generator lives at idle punctuated by surges, which inverter units handle efficiently and open-frame units handle loudly.

Power tools generator questions, answered

What size generator do I need to run power tools?

Size for your largest motor’s trigger surge. A 7-1/4 in circular saw — the standard site benchmark — cuts at ~1,400W and surges to ~2,300W at trigger pull; with 25% headroom that is 2,875W, the 3,500–4,500W class. A miter or table saw pushes the same math to roughly 4,500–5,000W. Rule of site thumb this calculator formalizes: one running big tool plus lights and a charger lives happily on 4,000W; two guys cutting simultaneously does not.

Can two tools run on the same generator at once?

Yes, with the staggered-start understanding: sum the running watts of everything on, then add only the LARGEST single surge — two saws almost never hit trigger at the same instant. Circular saw (1,400W) + shop vac (1,000W) running, plus the saw’s 900W surge delta, is ~3,300W peak: a 4,500W unit handles it. The failure mode is two 15A saws on one 3,500W generator with both triggers down — that is a running-watts problem no start-staggering fixes.

Why does my saw bog down on the generator but not on house power?

Voltage sag. House circuits sit on a stiff grid; a generator’s voltage dips when the surge hits, and a universal motor responds by losing torque and speed — which you feel as bogging. Fixes in order of cheapness: shorter/heavier cords (12-gauge minimum, 10-gauge past 50 ft), don’t start cuts during another tool’s surge, and if it persists, the generator is undersized for the tool’s real draw — check the nameplate amps against what you bought.

Has cordless changed the generator question?

Fundamentally. A crew on a battery platform (DeWalt 20V/60V, Milwaukee M18, Makita 40V) needs a generator only to feed chargers — 100–300W each, no surge — so a 2,000W inverter quietly charging a six-pack of batteries replaces the 4,500W unit entirely for many trades. Corded still rules for all-day high-draw tools (table saws, big compressors, demolition). The modern site pattern: small inverter + charger bank as the default, big generator only when a specific corded tool demands it.

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