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DIY Cost Tools

DIY Cost Tools

Inverter Size Calculator

Estimate continuous inverter capacity, surge rating, and DC input current from planned AC loads and headroom.

Use the units shown beside each field. Decimal and scientific notation are accepted for non-integer fields; blanks, commas, fractions and non-finite entries are rejected.

Minimum continuous rating1500 W
Minimum surge rating2500 W
Estimated DC current at continuous load55.55555556 A
Estimated DC current at surge115.7407407 A

The displayed results apply to the default example. Enable JavaScript to calculate other inputs.

How to use this calculator

  1. Replace the example values with measurements or ratings for the exact vehicle, circuit, component or system.
  2. Keep every value in the labeled unit and use manufacturer data where available.
  3. Select Calculate, then review the result together with the limitations and safety notes.

Formula and method

Continuous rating = continuous load × (1 + headroom). Surge rating is at least the larger of expected surge and continuous rating. DC current = AC watts ÷ voltage ÷ efficiency.

Calculations run in your browser. Results are hidden whenever an input changes or validation fails, preventing an older result from being mistaken for a new calculation.

Worked example

Continuous AC load = 1200 W; Largest expected surge = 2500 W; Capacity headroom = 25 %; Battery-system voltage = 24 V; Inverter efficiency = 90 %. The calculator returns Minimum continuous rating = 1500 W; Minimum surge rating = 2500 W; Estimated DC current at continuous load = 55.55555556 A; Estimated DC current at surge = 115.7407407 A.

The worked example uses the same defaults shown in the interface, allowing the formula and displayed result to be checked together.

Limitations and safety

Waveform, surge duration, temperature, wiring, fusing, battery limits and manufacturer ratings matter. Have high-current systems designed and protected by qualified people.

This is an educational planning model. Confirm ratings, tolerances, code requirements and safe procedures with manufacturers and qualified professionals before purchasing, modifying, wiring or operating equipment.

Frequently asked questions

Why can DC current be very high?

At low battery voltage, supplying the same power requires much more current, and inverter losses increase the required input further.

Why does the calculator reject my entry?

Each field shows its supported range. Whole-number fields reject decimals, and all fields reject blanks, words, comma-formatted numbers, fractions and non-finite values.

How should I use the displayed precision?

Keep extra digits while checking the calculation, then round to the precision supported by the measurements, component tolerances and published ratings.

Review notes and reference

Reviewed October 4, 2026. The formula and default example were checked together. The script was tested for defaults, input boundaries, invalid formats, condition-specific errors and recovery after an error. Reference: OSHA electrical safe-work requirements. Explanations and examples are original.

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