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Free planning tool Model 2026.08

Whole House Generator Sizing Calculator

Use this whole house generator sizing calculator to choose the loads that must run during an outage, replace planning values with nameplate watts, and see the complete calculation behind the recommended standby-generator tier.

Build my load plan See the 2,000 sq ft examples
  • Editable running watts
  • Motor-start calculation
  • Excel download

Interactive load worksheet

Generator sizing calculator: choose what must run.

Live result · No signup
Start with a presetThen replace placeholder watts with equipment nameplate data.
Essential loads
Planning basis

Internal planning allowance; replace it with a measured or panel-derived value when available.

Planning basis

Generac wattage worksheet planning value.

Planning basis

Internal planning allowance for small continuous electronic loads.

Planning basis

Generac buyer worksheet planning value.

Planning basis

Generac buyer worksheet planning value.

Planning basis

Internal planning allowance; use the motor nameplate for a real project.

Comfort loads
Planning basis

Internal bounded placeholder; actual compressor LRA, soft-start equipment, and fuel rating can materially change the result.

Planning basis

Generac wattage worksheet planning value.

Large electric loads
Planning basis

Internal planning allowance; verify the equipment nameplate.

Planning basis

Internal planning allowance; cooking diversity and local sizing methods vary.

Planning basis

Internal planning allowance; verify the equipment nameplate.

Planning basis

Internal planning allowance; use the configured charger amperage for a real project.

Custom equipment

02 A better square-foot answer

What size generator for a 2,000 sq ft house?

The honest answer is a load plan, not one universal number. These three examples keep the house size fixed and change only what must operate together. They use the same formula and 20% buffer as the calculator above.

Illustrative generator sizing scenarios for a 2,000-square-foot house
Outage planSelected runningLargest extra startWith 20% bufferPlanning tier
Essentials onlyLights, outlets, refrigeration, internet, security, and a gas-furnace blower.3,650 W2,350 W7,200 W10 kW
Managed comfortEssentials plus a sump pump and microwave, with large loads used selectively.6,200 W2,350 W10,300 W14 kW
Broader whole-home planManaged comfort plus a central-air planning load, before any electric heat or EV charging.9,700 W7,000 W20,100 W22 kW
Read the table carefully.

Central air, wells, electric heat, water heating, ranges, dryers, and EV charging can move the result quickly. Load management may keep some large appliances out of the simultaneous total. Fuel type and site conditions can also change a generator's usable output.

03 Visible calculation

How the sizing worksheet works.

  1. 1
    Add selected running watts.

    Count the loads expected to operate at the same time.

  2. 2
    Add one controlling startup load.

    Use the largest additional motor-start requirement, not every startup value combined.

  3. 3
    Add visible planning headroom.

    The default 20% buffer can be changed; it is a budgeting assumption, not an electrical-code rule.

  4. 4
    Round up to a supported tier.

    The worksheet chooses the first standard planning tier that is not below the rounded requirement.

Planning formula

Σ running W+largest extra start W+buffer

7,150+7,000+2,830= 17,000 W → 18 kW
Default worksheet example · values rounded for display

04 Work offline

Home generator sizing calculator for Excel.

Use the formula-driven workbook during equipment inventory or contractor conversations. Yellow cells are editable; formulas calculate selected running load, the largest additional starting load, buffer watts, and the next planning tier.

Download the Excel worksheet
GENERATOR BUDGET / .XLSX
01

Sizing Worksheet20 editable rows + live summary

02

Assumptions & SourcesTier lookup + evidence boundaries

Formula-driven · 11 KB · Reviewed 2026-08-05

05 Evidence boundary

Sources, assumptions, and limits.

Manufacturer material supports the worksheet sequence and selected example loads. Values labeled as internal planning allowances are bounded placeholders and should be replaced with equipment data for a real project.

01
Generac

Generator Wattage Worksheet

The running-watts plus single-largest additional-starting-watts worksheet method and selected household planning defaults.

Open source
02
Cummins

Home Generator Sizing Calculator

Adding the largest starting requirement to simultaneous running loads and retaining planning headroom.

Open source
03
Briggs & Stratton

Choosing a Home Generator

A 20% planning buffer and the importance of selecting the household loads that must operate during an outage.

Open source
Planning boundary

This result is not a contractor quote, electrical design, or equipment-selection approval. Final sizing must account for actual nameplates, motor-start characteristics, fuel-specific ratings, transfer equipment, conductors, load management, site altitude and temperature, and applicable local requirements.

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06 Plain-language answers

Generator sizing questions, answered.

Use the answers to plan the worksheet—not to replace a project-specific load calculation.

01What size generator does a 2,000-square-foot house need?

Square footage does not determine generator size by itself. In this planning model, selected essentials produce a 10 kW tier, managed comfort loads produce 14 kW, and a broader plan with central air produces 22 kW. Actual equipment, fuel rating, and simultaneous loads can change the answer.

02How does the generator sizing calculator handle starting watts?

It adds all selected running watts, then adds only the largest single additional starting requirement. It applies the selected planning buffer and rounds up to the next supported standby-generator tier.

03Should I add every appliance's starting watts together?

Not in this worksheet method. It assumes the largest motor startup is the controlling additional load rather than every motor starting simultaneously. A project with unusual sequencing or multiple simultaneous starts needs project-specific review.

04Can I use the Excel generator sizing worksheet offline?

Yes. The downloadable workbook contains editable load rows, formulas for running and starting watts, an adjustable buffer, a standard-tier lookup, and a separate assumptions-and-sources sheet.

05Is this an electrical load calculation?

No. It is an early planning worksheet for comparing outage priorities and budget scenarios. A qualified local professional must verify equipment nameplates, fuel-specific output, transfer equipment, conductors, load management, and applicable requirements.