SizeMyGenerator

Generator Sizing Calculator

Find the perfect backup generator for your home

Takes about 60 seconds • No email required

What do you want to power?
Step 1 of 5
Home details
Step 2 of 5
Used to estimate elevation & typical summer high. Leave blank to assume sea level & 60 °F.
NEC general lighting load = 3 watts per sq ft × this number. Include garage & basement.
Appliances & circuits
✅ Preset applied. 0 items selected.
Step 3 of 5
HVAC & EV loads
Step 4 of 5
❄️ Outdoor equipment
Add one row per outdoor unit and copy voltage, minimum circuit ampacity (MCA), and rated-load amps (RLA) from its nameplate. The planning load is the larger of MCA or RLA × voltage, in VA. Do not include LRA here; it belongs in the separate motor-start section.
🔥 Heating
🔌 EV chargers
Included at 100%. Enter each charger's actual charging power in kW (for example, 7.2 kW), not breaker amps.
⚡ Largest motor or compressor start
Required when an unmanaged sump, septic grinder, well or pool pump, A/C, or heat-pump outdoor unit is active. The calculator selects the largest screening estimate automatically; replace it with nameplate LRA or measured inrush when available.
Only active, unmanaged qualifying motors and outdoor units appear.
No qualifying starting load is active.
Enter nameplate LRA or verified measured inrush. A sourced estimate is provided when those data are unavailable.
Outdoor units use the greater of MCA or RLA. For pumps, use nameplate running current when available.
Soft-start reduction is not currently included without verified, equipment-specific performance data.
Peak startup replaces this source's running VA with starting VA. An existing soft starter is recorded here, but no generic reduction is applied; enter its verified measured inrush above.
Each eligible outdoor unit is managed by its stable equipment record. A/C condensers are removed only from cooling; heat-pump condensers are removed from cooling and applicable heat-pump-heating scenarios. Auxiliary electric heat remains a separate manageable load.
Settings & safety margin
Step 5 of 5
?
Default is 20%. Most homes use 10–30% headroom.

How to use this calculator

1

Choose your coverage level

Select whether you want to power essentials only, most of your house, or everything during an outage.

2

Enter your home details

Provide your ZIP code (for elevation/temperature adjustments) and square footage for accurate calculations.

3

Review & adjust appliances

We'll pre-select common appliances based on your coverage level. You can customize the list and wattages as needed.

4

Add HVAC, heating & EV chargers

Include any air conditioning units, heating systems, or electric vehicle chargers you want to power.

5

Get your recommendation

Use the summary card to see planning load, needed amps and peak surge, then talk to a licensed electrician.

Finding appliance wattage & starting amps

Look for the metal nameplate or data tag on your appliance (usually on the back or bottom).
Find "Watts" or "W" — this is the running wattage you'll enter here.
If only Amps and Volts are listed: Watts = Amps × Volts (e.g., 5A × 120V = 600W).
For motors/compressors, look for "LRA" or "Starting Amps" to use in the Max Starting Load section.
📸 Video tutorial and photo examples coming soon!
Heads up: This calculator is for general information only and does not replace a site visit or detailed load study. Always consult a licensed electrician and follow local codes before purchasing or installing a generator.

Planning to buy a generator?

Tell us what you are considering and when you expect to buy. We will review your information and reply with the most useful next step. You can also request local installer introductions as that service becomes available.

Fields marked Required are required.

Optional, but useful if you request installer introductions.

Tell us anything useful about your home, equipment, or outage needs.

No obligation. We will use your information to respond to this request and will share it with installers only when you select the installer-introduction option.