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Peak HP vs real watts: check any shop vac listing
Updated
Enter the peak HP from the title and the amps from the spec table. The calculator turns both into watts so you can compare them. Amps times volts is what the vac pulls from the wall. Peak HP times 746 is what the claim would need.
Peak HP reality check
An estimate. One horsepower is 746 watts. Amps times volts is the power the vac draws from the wall, and some of that is lost as heat and noise, so the real output is lower still. If a listing gives watts but no amps, divide the watts by 120 and enter that.
Why peak HP cannot be the running power
One horsepower is 746 watts. A standard household circuit is 15 amps at 120 volts, which is 1,800 watts, or about 2.4 HP if nothing were lost. Any shop vac that plugs into that outlet and claims more than 2.4 HP is quoting something other than running power.
The makers say so themselves. Shop-Vac's product pages define peak horsepower as "a term used in the wet-dry vacuum industry for consumer comparison purposes" and say it does not denote the operational horsepower but the output of a motor, including its inertial contribution, in laboratory testing. They add that in actual use the motors do not operate at the peak horsepower shown. Vacmaster's maker page for the 12 gallon VJH1211PF carries the same footnote.
For the real number, the maker of Vacmaster puts it plainly in its FAQ: multiply the amps of your vacuum by the voltage.
The seven picks, run through the same math
| Model | Peak HP | Claim in watts | Real watts | Where the real watts come from | Share | Most HP those watts could make |
|---|---|---|---|---|---|---|
| CRAFTSMAN 16 gal | 6.5 | 4,849 W | 1,440 W | 12 A and 1,440 W on the listing | 30% | 1.9 HP |
| Vacmaster 12 gal | 5.5 | 4,103 W | 1,416 W | 11.8 A and 1,416 W on the listing | 35% | 1.9 HP |
| Vacmaster Beast 5 gal | 5.5 | 4,103 W | 1,320 W | 11 A and 1,320 W on the listing | 32% | 1.8 HP |
| DEWALT 6 gal | 4 | 2,984 W | 864 W | 7.2 A on the listing x 120 V | 29% | 1.2 HP |
| Stanley 6 gal | 4 | 2,984 W | 1,200 W | 1,200 W on the listing | 40% | 1.6 HP |
| Vacmaster 5 gal steel | 4 | 2,984 W | 960 W | 960 W on the listing | 32% | 1.3 HP |
| Armor All 2.5 gal | 2 | 1,492 W | 720 W | 6 A and 720 W on the listing | 48% | 1.0 HP |
Peak HP x 746Real watts from the listing's amps or watts
- CRAFTSMAN 16 gal4,849 W1,440 W
- Vacmaster 12 gal4,103 W1,416 W
- Vacmaster Beast 5 gal4,103 W1,320 W
- DEWALT 6 gal2,984 W864 W
- Stanley 6 gal2,984 W1,200 W
- Vacmaster 5 gal steel2,984 W960 W
- Armor All 2.5 gal1,492 W720 W
Take the CRAFTSMAN 16 gallon. 6.5 x 746 = 4,849 watts claimed. The listing gives 12 amps and 1,440 watts. 1,440 / 4,849 = 30 percent. Even with a perfect motor, 1,440 watts is 1.9 HP.
When the listing disagrees with itself
- The DEWALT 6 gallon listing shows 7.2 amps and a wattage line of 135.5 watts. 7.2 x 120 = 864 watts, so the 135.5 cannot be electrical draw. The listing does not say what it is.
- The Stanley 6 gallon listing shows 1,200 watts and 3.7 amps. 1,200 watts at 120 volts is 10.0 amps.
- The Vacmaster 5 gallon steel listing shows 960 watts and 4.36 amps. 960 watts at 120 volts is 8.0 amps.
The rating label on the vac itself is the tie breaker. If you cannot see it before you buy, plan on the higher draw.
What the amps are good for
Amps tell you what the vac asks of your circuit, not how well it cleans. The two biggest picks draw about 12 amps each, which is most of a 15 amp circuit. ESFI lists often tripped breakers and dimming lights as warning signs of an overloaded circuit. For cleaning power, look at CFM, water lift and air watts instead.
Run any listing through the peak HP calculator, match a vac to your job with the job checker, or compare all seven picks on the roundup page.