Inverter Sizing Calculator Formula

Understand the math behind the inverter sizing calculator. Each variable explained with a worked example.

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Formulas Used

Minimum Inverter Rating

min_inverter_w = continuous_load_w * surge_multiplier

DC Input Current (continuous)

dc_current_a = continuous_load_w / (dc_voltage * eff_fraction)

DC Power Draw

dc_power_w = continuous_load_w / eff_fraction

Variables

VariableDescriptionDefault
continuous_load_wContinuous Load(W)500
surge_multiplierSurge Multiplier(x)2
inverter_efficiency_pctInverter Efficiency(%)90
dc_voltageDC Input Voltage(V)12
eff_fractionDerived value= inverter_efficiency_pct / 100calculated

How It Works

Inverter Sizing

Formulas

Inverter Rating = Continuous Load x Surge Multiplier

DC Current = AC Load / (DC Voltage x Efficiency)

Motors and compressors draw 2-3x surge at startup. Size the inverter for the surge, not just continuous load.

Worked Example

500 W continuous load, 2x surge, 90% efficient inverter on 12 V DC.

continuous_load_w = 500surge_multiplier = 2inverter_efficiency_pct = 90dc_voltage = 12
  1. 01Minimum inverter = 500 x 2 = 1000 W
  2. 02DC current = 500 / (12 x 0.9) = 46.3 A
  3. 03DC power = 500 / 0.9 = 556 W

Ready to run the numbers?

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