The numbers, from a manufacturer's chart
Champion publishes a wattage chart for exactly this purpose, and its figures are the ones this page uses. Two columns matter: what the tool draws while working, and what it demands in the moment the motor starts.
| Tool | Running watts | Starting watts |
|---|
| Electric drill, 1/2 in | 400-600 W | 800-1,200 W |
|---|
| Hammer drill | 900-1,200 W | 1,800-2,400 W |
|---|
| Reciprocating saw | 960-1,200 W | 1,920-2,400 W |
|---|
| Circular saw, 7-1/4 in | 1,200-1,800 W | 2,400-3,600 W |
|---|
| Miter saw, 10 in | 1,200-1,800 W | 2,400-3,600 W |
|---|
| Angle grinder, 4-1/2 in | 900-1,800 W | 1,800-3,600 W |
|---|
| Table saw, 10 in | 1,800-3,000 W | 3,600-6,000 W |
|---|
| Air compressor, 1 HP | 1,500 W | 4,500 W |
|---|
| Air compressor, 2 HP | 2,500 W | 7,500 W |
|---|
| Air compressor, 3 HP | 3,500 W | 10,500 W |
|---|
Figures from Champion Power Equipment's published generator wattage chart, linked below. Your specific tool states its amperage on the plate — multiply by 120 to get watts, as the nameplate guide explains.
The multiplier is the lesson
Look down the two columns and a pattern appears. Hand tools with universal motors — drills, saws, grinders — start at roughly twice their running draw. Air compressors, which have induction motors starting against pressure, want three times.
That is why a job-site generator is sized on the starting column. A 1 HP compressor that runs at 1,500W and starts at 4,500W will trip a 3,000W machine every time it kicks in, no matter how gently you use it. The starting-watts page covers why induction motors behave this way.
Sizing for a real site
Nobody runs one tool. The honest method is: take the largest starting figure on site, then add the running watts of everything else that will be on at that moment.
| Setup | Worst-case demand | Generator size |
|---|
| Drill, work light, charger | ~1,400 W at start | 2,000 W is enough |
|---|
| Circular saw plus light and charger | ~3,900 W at start | 4,000-4,500 W |
|---|
| Table saw plus a light | ~6,200 W at start | 6,500 W or more |
|---|
| 2 HP compressor plus a saw running | ~9,300 W at start | 9,500 W or more |
|---|
Worst case is the largest starting figure plus the running draw of everything else. The arithmetic uses the upper end of each published range, which is how sizing should be done.
For a full kit list and machines sized to it, see the job-site generator roundup and the job-site scenario page.
Can a battery run power tools?
Partly, and the honest split is useful.
What batteries do well: charging cordless tool packs, running LED work lights, powering a laptop or a small radio, and short bursts from a drill or a reciprocating saw. All of that fits inside 1,800W with room, and it happens indoors without fumes.
What batteries do badly: sustained cutting with a corded saw, anything with a compressor, and a full day of it. The energy is the problem as much as the output — a circular saw at 1,500W drains a 1kWh battery in about 35 minutes of actual cutting, and the surge at each start eats into the inverter's headroom.
A sensible site setup is both: a generator for the corded tools and a battery for the electronics and the charging, which keeps the noisy machine off for most of the day.
Watch the extension cord
Tool sizing goes wrong at the cord as often as at the generator. A saw pulling 15A through 100 feet of thin cord loses voltage, and a motor starved of voltage draws more current and runs hot.
Use 12-gauge for long runs at tool loads, keep the run as short as you can, and uncoil the cord completely — the cord guide covers gauge against distance.
The short version
- Hand tools start at about 2x their running watts; compressors at about 3x.
- A circular saw is a 3,600W start. A 10 inch table saw can be 6,000W.
- Size on the biggest start plus everything else running.
- Batteries charge tools and run lights; generators run saws and compressors.
