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Generator Size Calculator

Decision support

What this tool helps you decide

Best for

Generator size screening for selected household loads.

Enter

Running watts, starting watts, simultaneous loads and generator efficiency assumptions.

You get

Estimated running and surge demand with a size range.

Check before buying

Motor starting behavior, transfer equipment, fuel, ventilation and licensed installation still need review.

What you will get

1. Needed

See the estimated project quantity from your measurements.

2. Buy

Add waste and round to complete bags, boxes, cans, bundles or delivery quantities.

3. Check

Review product coverage, site conditions, local requirements and supplier details before ordering.

Quick answer: Estimate generator running and starting watts from household or jobsite loads. Start with actual measurements, use the product label for coverage or yield, and treat the result as a planning estimate until site conditions and supplier requirements are confirmed.

Estimate generator capacity from running watts, starting watts and a planning reserve.

Formula

Peak planning load = running load + largest starting surge. Apply reserve, then compare with the generator's rated running and starting output.

Safety note: Transfer equipment, grounding, fuel, ventilation and electrical connection require qualified installation.

Practical planning notes

How to use this Generator Size Calculator

Estimate generator running and starting watts from household or jobsite loads. Start with the actual dimensions or load values from the project, keep the units consistent, and change the default assumptions when the product label or supplier sheet gives you a more accurate value.

What the estimate does and does not include

This page is for early material planning. The result can change with openings, layout, cuts, waste, product yield, density, packaging, access, installation method and site conditions. It does not replace structural design, permitted drawings, manufacturer instructions or a contractor quotation.

Worked planning example

For a simple project, enter one measured section first and review the result. If the shape is irregular, split it into smaller sections, calculate each section, and add the quantities before applying whole-bag, box, bundle or delivery rounding.

Before you order

  • Re-check the field measurements and the unit labels.
  • Replace generic coverage, yield, density or spacing assumptions with the exact product data.
  • Confirm package size, minimum order, delivery, tax and local requirements with the supplier.