How to size an industrial generator

Published October 3, 2026.

The math here is a cord-and-plug tool list from Honda's contractor chart. A building, a three-phase service, or a life-safety system is an engineer's load study.

Quick answer: Honda lists a 10-inch table saw at 4,500 starting watts and 1,800 running watts, and a 1 hp high-pressure washer at 3,600 starting watts and 1,200 running watts. Both on, 20% headroom, the calculator recommends 7,000 W. The peak is 5,700 W. That is a jobsite portable class, not a facility rating.

The two rows, and only those two

Load	Running watts	Starting watts
Table saw, 10 in.	1,800	4,500
High-pressure washer, 1 hp	1,200	3,600

Honda's contractor section has more rows than these two: air compressors, circular saws, drills, and motor horsepower bands. Each of those already has, or can take, its own one-appliance page. This page adds the saw and the washer because their starting watts are not equal, so the formula's choice of "largest start" does not depend on which row you type first. A 1 hp air compressor is also 4,500 W starting on Honda's chart, the same start as the saw. Two equal starts make the extra-surge result depend on order. This pair does not.

The single-tool pages are table saw, pressure washer, and air compressor. Use the row that matches the nameplate. Honda's 1,800 W saw running figure is not Champion's higher running band, and this page does not mix the two charts into one total.

Worked example

Both tools running, headroom 20%. Same steps as sizeGenerator():

Running total = 1,800 + 1,200 = 3,000 W.
Largest start is the saw at 4,500 W. Extra surge = 4,500 − 1,800 = 2,700 W. The washer's gap, 3,600 − 1,200 = 2,400 W, is not added.
Peak = 3,000 + 2,700 = 5,700 W.
5,700 × 1.20 = 6,840 W, rounded up to the next 500 W = 7,000 W recommended.

The generator's running rating has to clear 7,000 W. Its starting rating has to clear 5,700 W. Gasoline at 50% of the recommendation is 7,000 / 7,000 = 1.0 gallon per hour, so a 4 gallon tank lasts 4.0 hours. That is the portable rule, not a jobsite fuel test. Replay the two custom rows on the calculator.

If the washer is off while the saw starts, the saw alone is a smaller list. This page sizes them together because that is the stricter case. Turning one off is a sequencing choice. The home sequencer uses the same highest-start extra as the list above, then stages rows into lanes. That staged result is not the everything-on math above. It lives on the load sequencer.

When the formula is the wrong tool

Stop and hire an engineer, and a contractor who does generator service, when any of these is true:

The load is a building service, a panel, or a process line, not a cord-and-plug tool whose watts are on a published chart.
Motors are three-phase, or the set has to carry elevators, fire pumps, or other life-safety equipment.
The connection is an automatic transfer switch into a facility, not an extension cord at a saw.
The nameplate is missing and the only number available is a guess.

This site does not invent a kilowatt rating for a plant. Finding a commercial generator service is the hiring page. OSHA 3286 says not to attach a generator to a structure's electrical system unless a qualified electrician installs a transfer switch. That sentence does not become optional because the load is a table saw inside a building.

A common mistake

Adding both starting watts on top of the running total: 4,500 + 3,600 + 3,000 = 11,100 W, then adding 20% again. The saw's 4,500 already includes its 1,800 W of running draw. The formula adds only the 2,700 W gap, once. The other mistake is treating a 10-second "starting boost" printed on a generator as if it were a continuous 7,000 W rating. The recommendation above is a continuous class. A short boost that expires does not replace it.

Limits, and when to call a pro

Check voltage on the tool. The watt steps do not choose 120 V or 240 V for you. A portable set on a job still goes outdoors. CPSC says at least 20 feet from homes and buildings, exhaust away from openings. OSHA's 3–4 feet of clear space around a portable generator is ventilation clearance, not a shorter distance to a wall opening. Both lines are spelled out on how to run a generator safely.

Permanent installation takes a licensed electrician and a permit where local code requires one. If the tool list grows past published chart rows, or the set feeds a building, the 7,000 W figure is no longer the design.

Compiled with AI assistance from the sources below. Spot an error? Email [email protected].

Sources

Honda, What wattage generator do I need? — contractor rows for the 10-inch table saw and the 1 hp pressure washer
OSHA 3286, Using Portable Generators Safely
CPSC, generator carbon monoxide warning