Battery, energy & solar
Inverter Size Calculator
Inverter planning starts with the sum of running watts and the largest added startup demand. The continuous estimate applies the entered reserve to the running total.
Aggregate running and surge loads, then apply your own headroom and efficiency assumptions.
Calculated result
Inverter planning totals
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
What this calculator returns
Compare continuous and surge requirements with the inverter manufacturer's ratings and time limits.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Running W = Σ(W × qty); peak W = running total + largest added startup demand; planned continuous W = running × (1 + headroom).
- V
- Nominal battery or bank voltage.
- Ah
- Charge capacity in amp-hours.
- Wh
- Nominal or usable stored energy in watt-hours.
- W
- Average load power in watts.
- η
- Entered conversion efficiency.
Starting multipliers and headroom are user-entered planning assumptions.
Worked example
| Input | Value |
|---|---|
| Loads | See the example load list in the calculator |
| Result | A 120 W laptop plus an 800 W pump with a 3× startup multiplier produces 920 W running and a 2,520 W single-start peak. |
A 120 W laptop plus an 800 W pump with a 3× startup multiplier produces 920 W running and a 2,520 W single-start peak.
Reference table
| Appliance | Planning watts | Use note |
|---|---|---|
| LED lamp | 10 W | Nominal example |
| Laptop computer | 60–120 W | Typical planning range |
| Refrigerator while running | 100–250 W | Cycling load; startup can be higher |
| Microwave oven | 900–1,500 W | Input varies by model |
| Portable space heater | 1,500 W | Common high setting |
| Electric kettle | 1,200–1,800 W | Varies by market and model |
Frequently asked questions
Is this inverter-size result code compliant?
No. PowerTotals performs transparent electrical math and planning estimates. Installation decisions must be checked against equipment documentation, the adopted code, and the authority having jurisdiction.
Are my inputs uploaded?
No. Calculations run locally in your browser, and analytics never receives raw electrical values.
Assumptions and limitations
- No authoritative appliance presets.
- No conductor, breaker, fuse, or protection sizing.
- Assumes one highest-surge load starts at a time.
Method and sources
Read the calculation methodology, review the technical sources, or browse the reference table index. Last reviewed .