Generator Sizing & Budget Calculator
Size a home generator from the appliances you need in an outage and see an itemised low, typical and high budget for a portable or standby install.
Your inputs
Results
Typical project budget
$10,750.00
- Low-end budget
- $8,600.00
- High-end budget
- $15,050.00
- Recommended generator size
- 10 kW
- Calculated requirement
- 9.53 kW
- Total running load
- 7,100 W
- Peak load when the largest motor starts
- 14,300 W
- Running load as % of generator rating
- 71%
≈Estimate based on the stated model and assumptions
| Load | Running watts | Starting watts |
|---|---|---|
| Central air conditioner | 3,600 | 10,800 |
| Refrigerators and freezers | 400 | 800 |
| Sump pump | 800 | 2,400 |
| Furnace blower | 800 | 2,300 |
| Lighting, electronics and small appliances | 1,500 | 1,500 |
| Item | Low | Typical | High |
|---|---|---|---|
| Generator | $3,840.00 | $4,800.00 | $6,720.00 |
| Transfer switch or inlet kit | $960.00 | $1,200.00 | $1,680.00 |
| Electrical work | $1,440.00 | $1,800.00 | $2,520.00 |
| Fuel connection | $880.00 | $1,100.00 | $1,540.00 |
| Pad and site preparation | $560.00 | $700.00 | $980.00 |
| Permit and inspection | $400.00 | $500.00 | $700.00 |
| Delivery and commissioning | $520.00 | $650.00 | $910.00 |
Inputs are never added to links for financial, salary or health calculators.
What if?
Pick an input and drag the slider to see how the result changes.
What this calculator does
A generator has to carry two numbers: the load of everything running together, and the brief surge when the biggest motor — usually the air conditioner or a pump — starts. This tool adds up the loads you select, applies a safety margin, rounds up to a standard residential size and then prices the equipment and installation work in ranges rather than a single figure.
Formula and method
Worked example
Calculated by this tool with its default inputs:
Inputs
- Central air conditioner: 3 tons
- Air conditioner has a soft-start kit: No
- Refrigerators and freezers: 2
- Sump pump: Yes
- Well pump: No
- Furnace blower: Yes
- Electric water heater: No
- Electric range or oven: No
- Lighting, electronics and small appliances: 1500 W
- Other running load: 0 W
- Safety margin: 20 %
- Installation scope: Standby generator — essential circuits
- Fuel connection: Natural gas (existing line)
- Local labour cost level: Average area (×1.0)
Results
- Typical project budget: 10,750
- Low-end budget: 8,600
- High-end budget: 15,050
- Recommended generator size: 10 kW
- Calculated requirement: 9.53 kW
- Total running load: 7,100 W
How to read the results
If the required kW falls just above a standard size, the next size up gives you room to add loads later. The low and high budgets bracket typical project prices; site conditions such as long gas runs, trenching or panel upgrades can push a real quote above the high figure.
Assumptions and limitations
- This is a planning aid, not a contractor quote or an electrical design. Load figures are typical values; check the nameplate of your own equipment.
- Costs are rough US-dollar planning ranges for US homes. Equipment is priced the same everywhere; installation items scale with the local labour level you choose.
- Installation normally needs a licensed electrician, a permit and, for gas, a licensed fitter. Never connect a generator to a home without a transfer switch or interlock.
Financial results are estimates based on the inputs and assumptions shown. They are not financial advice; confirm figures with your lender, provider or a qualified adviser before making decisions.
Questions
Why does the air conditioner dominate the result?
An air-conditioner compressor can draw about three times its running power for a moment when it starts. A soft-start kit cuts that surge and often lets you choose a smaller generator.
Should I size for the whole house or only essential circuits?
Essential-circuit systems cost less and need a smaller generator; a whole-home system runs everything but needs a larger unit and a service-rated transfer switch.
Does the result include fuel?
No. It covers buying and installing the system. Natural gas needs an adequate gas line; propane needs a tank, which is included when you choose propane.
Methodology and verification
- Result type
- Estimate based on the stated model and assumptions
- Formula version
- 1.0
- Automated verification
- 4 reference and validation test cases, checked against independently computed values. The site cannot be built if any of them fail.
- Editorial review
- Awaiting human editorial review. The explanation was drafted with AI assistance; the formula and examples are verified by the automated tests above.
Privacy
Everything you enter is calculated in this browser and is not sent to Numerith or anyone else. Because this calculator can involve personal financial or health details, your inputs are never added to share links or saved to history. Privacy policy