What Size Generator Do You Need to Run a 15 Amp Table Saw?

Two answers go around: about 4,000 W to start a table saw, or 6,300 W. Both come from generator makers' charts, and the gap is not about saws. It is about one column heading. Honda prints a table saw at 4,500 W "for starting", a total. Generac prints the same 1,800 and 4,500 under "Additional Starting Watts", and the arithmetic on its worksheet adds them. Below, the charts are read by their own rules and checked against the one number the saw maker does publish, 15 A.

The saw's own number: 15 A at 120 V

Every corded saw carries its rated amps on the nameplate. The common 15 A class covers all three saws in question: DeWalt lists its DWE7491RS jobsite table saw with a "15 amp motor" at 120 V, Makita lists its 5007MG 7-1/4 in circular saw at 15 A, and the 12 in miter saws compared in the 10 in blade on a 12 in miter saw guide are all 15 A machines.

Watts are volts times amps. The 2010 wattage worksheet on Home Depot's servers says so in as many words: if the running watts are not on the tool, "you may estimate using the following equation: WATTS=VOLTS x AMPS."

120 V x 15 A = 1,800 W

Honda uses the same conversion, listing its EU2200i as "1800 watts rated (15A)". On paper a 15 A saw and a 1,800 W rated generator match exactly, with nothing left over.

The nameplate does not give the starting draw, and none of the three product pages lists one. For that, the only published numbers are generator charts.

What five charts print for saws

Here is every saw row in five published charts, with each chart's own column heading. Running watts come first, then the starting figure exactly as printed.

The two Home Depot-hosted documents and Generac's jobsite chart carry identical saw rows, so they are three printings of one table, not three estimates. Generac's catalog also disagrees with itself: 1,800 and 4,500 in the worksheet, "Table Saw, 10"" 2,000 and 2,000 in the chart below it. And Generac's worksheet pair is exactly Honda's pair, as is the circular saw's 2,300. Only the heading above the second number differs.

Total or additional: the heading that changes the answer

A worksheet that says "additional" means the figure goes on top of the running watts. Generac's instructions: "Select the one device with the highest starting watts. Add that number to the the total running watts to determine the total wattage requirement." The Home Depot-hosted worksheet and Champion's flyer use the same method, Champion with "Add the HIGHEST SINGLE Starting Watt to Total Running Watts needed."

Honda's column works differently, and its own rows prove it. Loads with no motor, which need no extra power to start, are listed with the same number in both columns: an electric fry pan at 1,800 and 1,800, an 8 in range element at 2,100 and 2,100. If the starting column were additional, a fry pan would need 3,600 W to switch on. It is a total.

Now put every chart on the same footing, the watts the generator must deliver at the moment the saw starts:

Five of the six table saw figures fall between 4,000 and 4,500 W. The 6,300 W outlier uses the same 4,500 Honda prints as a total, placed under a heading that tells the reader to add the running watts to it again.

The Sportsman guide shows how easily the two readings mix. Its worksheet columns say "ADDITIONAL STARTING WATTS" and its example adds a furnace fan's 2,350 to 4,250 running watts. Its own note then says that a refrigerator "requires 2200 starting wattage with a 700 running wattage, so you would need a generator with at least 2200 watt maximum output to run ONLY a refrigerator." Additional would mean 2,900 W. The guide reads its own column as a total in one paragraph and as additional in the next.

Which figure to trust, and why

Running: the nameplate. The chart makers defer to the tool themselves: "For exact wattages, check the data plate or owner's manual on the item you wish to power," says the Home Depot-hosted worksheet. On the table saw the charts agree with the plate, at 1,800 to 2,000 W. On the circular saw they list 1,400 to 1,500 W, while a 15 A saw like the Makita 5007MG is 1,800 W on its plate. Use the plate.

Starting: 4,500 W total. No saw maker publishes a starting draw, so this number has to come from a chart. Take 4,500 W because it is the highest figure once each chart is read by its own heading, so it covers all the others, and because it comes from the only chart whose starting column its own rows show to be a total.

Why not 6,300 W. Nothing in any chart supports a separate 4,500 W on top of the running watts for a table saw. The 6,300 figure appears only where Honda's 4,500 sits under Generac's "additional" heading, and Generac's own jobsite chart in the same catalog asks for 4,000 W.

Where 4,500 W could still be short. Honda Australia's brochure says appliances with electric motors "can draw up to three times their running load for a few seconds." Three times 1,800 W is 5,400 W. That sentence names air conditioners, fridges and pumps, not saws, and the same brochure lists a power saw at only "1500-2000" W. But it is the reason to treat 4,500 W as a floor rather than a target.

Generators measured against the threshold

Generators publish two ratings. In Generac's words, running watts are "the amount of power the portable generator can produce continuously" and starting wattage is "the power that the generator can produce for short periods of time." Here are published ratings from the Honda and Generac catalogs against the saw's 1,800 W running and each chart's starting total.

Honda describes the EB5000X's extra rating, iAVR, as letting the generator "operate well above its maximum rating for up to 10 seconds to start high initial amp draw situations." The Home Depot-hosted worksheet says starting watts are needed "for two to three seconds", so a 10 second rating covers the start with time to spare.

Below 4,000 W maximum, no chart says the saw will start. At 4,500 W, every chart read by its own heading is met.

Adding the rest of the shop

A saw rarely runs alone. The charts add every running load, then the single largest starting figure. With Honda's total for the saw, that total replaces the saw's running watts at the moment it starts.

Worked example: the table saw, a 6 A shop vacuum already running, and a 300 W halogen work light.

• Vacuum: 120 V x 6 A = 720 W, by the worksheet's volts-times-amps rule.
• Work light: 300 W, the worksheet's row for a 300 W quartz halogen light, with no starting watts.
• Running total with everything on: 1,800 + 720 + 300 = 2,820 W.
• At the instant the saw starts: 720 + 300 + 4,500 = 5,520 W.

That rules out the 4,000 and 4,500 W maximum machines in the table above. The EB5000X covers it on its 10 second rating and the GP5500 on its 6,875 W starting rating. The vacuum's own start is not in this figure because it was already running, and no chart here lists a shop vacuum's starting draw.

An air compressor is the bigger load. Honda lists a 1 HP compressor at 4,500 W to start and 1,600 W running, and Generac prints the same pair under its additional heading. With the saw running and the compressor kicking on, Honda's figures give 1,800 + 4,500 = 6,300 W. How often that kick happens depends on the tank and the pump, as worked out in whether a bigger compressor tank gives more CFM.

On a 120/240 V generator, check how its power reaches the 120 V outlets. Honda says the voltage selector's "120 volt mode allows generator's full power to be available at all 120 volt receptacles."

The cord between the generator and the saw

A generator is a receptacle like any other, so the saw makers' cord tables still apply, 12 gauge to 50 ft for a 12 to 16 A tool, as set out in what gauge extension cord a 15 amp tool needs. Those tables are sized at running current, and the start draws more.

Using the copper resistance figures on that page, a 50 ft 12 gauge cord has 100 ft / 1,000 x 1.59 = 0.159 ohm of conductor, out and back. If the 4,500 W starting load is drawn at 120 V, the current is 4,500 / 120 = 37.5 A.

The worksheet's own caution says damage may result if equipment "is not designed to operate within a +/- 10% voltage variation" from the generator's nameplate. On a 100 ft 12 gauge cord, the cord alone uses up that 10 percent during the start. Every figure in the table is copper at 20 C, so real cords drop slightly more.

The practical rule follows: keep the cord inside the saw maker's table, 50 ft of 12 gauge at most. Generator watts do nothing for the volts lost in the cord. For a cut far from any power, a cordless saw has no cord drop at all, and its packs compare on watt hours, as whether 20V MAX is the same as 18V works out.

Where this answer stops applying

• Saws above 15 A or on 240 V. Cabinet saws with 240 V motors and saws rated above 15 A are outside every chart row here. Use the nameplate for running watts, and expect the 120 V starting figures not to carry over.
• Saws with soft start. No chart here has a row for a soft start saw, and no published figure here says how much less one draws at start. Size it like any other 15 A saw.
• Published ratings only. The generator table compares catalog ratings with chart figures. It is not a claim about how any unit behaves under a particular saw.
• Where the generator runs. Honda's catalog: "Never run a generator in an enclosed or even partially enclosed area." So the generator sits outside and the cord comes in, which is where the 50 ft limit above starts to bind. A receptacle-equipped bench near the door, as planned in the garage shop layout, keeps the run short. Keep its fuel the way carrying a gas can in a truck tool box sets out.

The thirty-second check

1. Read the saw's nameplate amps. At 15 A and 120 V, the running load is 1,800 W.
2. Add the running watts of everything else that will be on at the same time.
3. Add 4,500 W for the saw's start, replacing its 1,800 W running figure in that moment. If another motor has a bigger start, use that one instead.
4. Buy a generator whose running rating covers step 2 and whose starting or maximum rating covers step 3. For the saw alone, that is 1,800 W running and 4,500 W starting.
5. Keep the cord at 12 gauge and 50 ft or shorter. A bigger generator does not fix voltage lost in a long cord.