Calculator · Electrical & power for tools
Inverter size calculator for power tools
Pick the tools you will run at the same time. We add the running watts and the largest starting load, then give the inverter rating and the 12 V battery draw.
Calculator
1. Add the tools you will run at the same time
- Circular saw, 7-1/4" (1,400 W run + 2,300 W to start)
2. Your result
Your answer
with at least 4,100 W surge. That covers 1,400 W running and a 3,700 W peak when the biggest motor starts.
How the math works
- Continuous = total running watts × 1.2, rounded up to the next 100 W.
- Surge = (total running watts + the largest additional starting watts) × 1.1, rounded up. Only one motor starts at a time.
- 12 V battery draw = running watts ÷ 12 ÷ 0.85, allowing for about 85% inverter efficiency.
Check how long the inverter holds its surge rating. Some hold it for under a second, which may not start a motor. A pure sine wave inverter is the safe choice for tools with motors.
Wattage reference table
These are the presets the calculator uses, from two published charts. Both list additional starting watts: the extra power on top of running watts while a motor starts. Your tool's nameplate is the better number; enter it as "Your tool".
| Tool | Running watts | Additional starting watts | Source |
|---|---|---|---|
| Circular saw, 7-1/4" | 1,400 | 2,300 | Lowe's |
| Circular saw | 1,500 | 2,000 | Champion |
| Miter saw, 10" | 1,800 | 3,300 | Lowe's |
| Table saw, 10" | 2,000 | 2,000 | Lowe's |
| Table saw | 1,800 | 2,500 | Champion |
| Hand drill, 1/2" | 600 | 900 | Lowe's |
| Hammer drill | 1,000 | 3,000 | Champion |
| Angle grinder | 800 | 2,400 | Champion |
| Bench grinder, 8" | 1,400 | 1,100 | Lowe's |
| Belt sander, 3" | 1,200 | 2,400 | Lowe's |
| Reciprocating saw | 960 | none listed | Lowe's |
| Air compressor, 1 HP | 1,400 | 3,600 | Lowe's |
| Air compressor, 1/2 HP | 1,000 | 2,000 | Lowe's |
| Airless paint sprayer, 1/3 HP | 600 | 1,200 | Lowe's |
| Quartz halogen work light | 1,000 | none listed | Lowe's |
Worked example
One 7-1/4" circular saw from the Lowe's chart: 1,400 W running and 2,300 W additional starting. Continuous: 1,400 × 1.2 = 1,680, so 1,700 W. Surge: (1,400 + 2,300) × 1.1 = 4,070, so 4,100 W. Battery draw: 1,400 ÷ 12 ÷ 0.85 ≈ 137 A.
Questions people ask
Can a 1,000 W inverter run a circular saw?
No. Published charts list a 7-1/4-inch circular saw at 1,400 to 1,500 W running before it even starts.
Why does the surge time matter?
Some inverters hold their surge rating for less than a second, which may not be long enough to start a motor. Check the spec sheet.
Sources
- Lowe's portable generator wattage worksheet (running and additional starting watts)
- Champion Power Equipment: choosing a generator, quick reference wattage
- Samlex inverter FAQ: motor surge and surge duration (reposted by CARiD)
- Carbon monoxide information center (U.S. Consumer Product Safety Commission)
Change log: Nov 6, 2026: Rebuilt to spec: sourced reference data, formulas and worked examples; no unverified people or test claims.