Undersized inverters trip on motor starts; oversized units waste money and idle draw. This inverter sizing calculator takes your peak load in watts and a safety margin percent to recommend a minimum inverter rating for planning.
Benefits
- Minimum W = peak load × (1 + margin ÷ 100).
- Default margin covers modest surge and future loads.
- Outputs a watt target before you shop continuous vs. peak specs.
How it works
- Sum steady-state watts for appliances on the inverter bus.
- Enter peak load W and a safety margin percent.
- Read minimum inverter size in watts—match to datasheet continuous rating.
FAQ
How does an inverter sizing calculator work?
Multiply peak load watts by one plus the margin fraction: inverter W = peak W × (1 + margin ÷ 100). Example: 1,800 W peak with 25% margin → 2,250 W minimum. Use running watts for steady loads; raise margin when fridges, pumps, or power tools start on the same bus.
What is a good safety margin for inverter sizing?
20–30% is common for mostly resistive loads. Motor-heavy rigs often need 35–50% margin—or a separate surge calculator—because compressors can draw 2–3× at startup. Document which loads can start together before finalizing the SKU.
Continuous watts vs. peak (surge) on the datasheet?
This calculator targets minimum continuous watts after margin. Inverter labels also list peak/surge watts for motor starts. Pick a unit whose surge rating covers your largest starting load even when continuous watts meet the calculated minimum.
Technical specifications
- Minimum inverter W = peak_W × (1 + margin% ÷ 100).
- Peak load = sum of simultaneous running watts.
- Motors may need extra surge headroom beyond margin %.
- Related: inverter-sizing, watts-to-amps, battery-bank-size, ups-runtime.
Start from simultaneous peak load, not nameplate guesses
An inverter sizing calculator needs the watts that can be on at once—not every device in the house. Add running watts for loads on the inverter bus during your worst-case scenario: evening kitchen plus router, or workshop tool plus lights. That peak becomes the base before margin is applied.
Margin covers surge, efficiency loss, and growth
A 25% margin turns 1,800 W into 2,250 W—a cushion for brief overloads, inverter conversion loss, and one extra appliance later. Resistive-heavy loads may sit at 20%; vans with fridge compressors or well pumps should test higher margins or model motor surge separately before buying.
Match the result to real inverter labels
Calculated watts are a floor for continuous rating. Compare against vendor continuous and peak columns, split-phase needs, and charger pass-through if applicable. Chain to Watts to Amps for DC cable sizing at the battery, or Battery Bank Size when runtime must support the newly sized AC load.