Inverter Sizing Calculator for Construction Loads

Enter tools, lighting, pumps, and mixers easily. Get recommended inverter size, surge rating, battery draw. Download results for bids, planning, and safer installations always.

Inputs
Add all site loads you expect to run from the inverter.
Common values: 120, 230, 240, 277.
If unsure, use 0.9 for mixed loads.
Typical range: 15–30% for job sites.
Higher DC voltage reduces cable current.
Common range: 85–94% depending on load.
Used for battery capacity estimate.
Example: 80% allows deeper cycling.
Accounts for storage and conversion losses.
Loads List
Item Qty Running (W) Start Mult
Start Mult is the starting surge multiplier. For motor loads, typical values range 2–6.
Example Data Table
Use this example to understand common construction loads.
Example Load Qty Running (W) Start Mult Notes
Rotary hammer 1 1200 1.2 Power tools usually have mild surges.
Work lights (LED) 6 60 1.0 Lighting surges are typically minimal.
Submersible pump 1 750 3.0 Motor starting can dominate inverter sizing.
Formula Used
1) Running Power (W)
Sum each load’s running watts multiplied by quantity.
Total Running W = Σ(qty × runningW)
2) Starting / Surge Power (W)
Estimate each load’s starting watts using a multiplier.
StartW(each) = runningW × startMultiplier
Surge W ≈ Σ(max(runTotalW, startTotalW))
3) Apparent Power (VA)
Convert watts to volt-amps using the assumed power factor.
Running VA = Running W ÷ PF
Surge VA = Surge W ÷ PF
4) Safety Margin
Apply a margin to cover uncertainty and future additions.
Needed VA = VA × (1 + margin%)
5) Battery Sizing (Ah)
Estimate amp-hours needed for a target runtime.
Ah = (RunningW × hours) ÷ (Vdc × invEff × battEff × DoD)
How to Use This Calculator
  1. List every device you plan to run from the inverter.
  2. Enter quantity and running watts for each device.
  3. Set a start multiplier for motors or compressors.
  4. Choose power factor and a realistic safety margin.
  5. Select DC system voltage and efficiency assumptions.
  6. Press Calculate to view the recommended inverter sizes.
Practical note: This tool estimates electrical demand. Always confirm wiring, protection, and grounding requirements for your site conditions.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.