A home generator sizing calculator turns your appliances into a practical generator capacity recommendation using three connected values: kW, kVA and amps. For single-phase home systems, kW ≈ kVA because the power factor is close to 1.0.
The real electrical power your home appliances consume while operating. This is what you pay for and what your loads actually use.
The total apparent power the generator must provide. For single-phase homes, kW and kVA are essentially equal — a 10 kW house needs a 10 kVA generator.
The current at your selected voltage, useful for cable, breaker and transfer-switch planning.
The calculator combines your running loads, the starting surge of the largest motor (refrigerator, AC, well pump), a 15–25% safety margin, and your system voltage and frequency. The result is a usable generator recommendation rather than a simple total-load estimate.
Works with 110/120 V and 220/240 V single-phase systems at both 50 Hz and 60 Hz.
Select from common home appliances with pre-filled running and starting watts, or enter custom loads.
Recommendations map directly to ShanHua generator sets from 8 kVA to 4,000 kVA — with fuel and runtime estimates included.
Use the calculated requirement as the basis for a factory-direct quotation — no obligation.
Choose Appliance Mode for accurate load-based sizing or Detailed Mode for more advanced inputs. Both methods estimate the generator capacity required to handle running load, motor starting demand and your selected operating conditions — on single-phase 110/120 V or 220/240 V systems.
Add the appliances you need to keep running during an outage. Starting surge is automatically included for motor-driven equipment.
Enter your total load, motor details and site conditions for a more precise sizing estimate.
Most homes fall into predictable size ranges depending on square footage and whether you want essential backup or whole-home coverage with air conditioning. Use this table as a quick reference to check whether your calculator result is in a realistic range.
| Home Size | Essential Backup | With Central Air Conditioning |
|---|---|---|
| Under 1,200 sq ft (110 m²) | 3–5 kW | 8–10 kW |
| 1,200–2,000 sq ft (110–185 m²) | 5–8 kW | 10–15 kW |
| 2,000–3,000 sq ft (185–280 m²) | 8–12 kW | 15–22 kW |
| Over 3,000 sq ft (280+ m²) | 12–15 kW | 22–30 kW |
If you prefer to work the numbers by hand — or want to verify the calculator result — follow this five-step method to move from your appliances to a practical generator rating.
Write down every appliance, motor and piece of equipment that may operate at the same time during an outage. Record the running watts from the nameplate or spec sheet.
Express all loads in watts or kilowatts. For motors, 1 HP ≈ 746 W. For single-phase home systems, kW ≈ kVA because power factor is close to 1.0.
Add the continuous power requirement of all appliances expected to operate simultaneously. This establishes your home's normal connected running demand.
Find the motor-driven appliance with the highest startup requirement (AC, well pump, refrigerator) and add its additional starting demand so the generator can handle the transient without tripping.
Add an allowance for transient demand and future growth. A planning factor of 1.15–1.25 is commonly used for home applications, subject to your actual requirements.
A home with refrigerator (700 W), well pump (1,500 W), furnace fan (800 W), lights (400 W) and Wi-Fi (20 W) totals 3,420 W running. Add the largest surge — well pump at 4,500 W — giving 7,920 W. Apply 1.2 safety factor → 9.5 kW. For single-phase, kW ≈ kVA, so a 10 kVA / 10 kW diesel generator is the right recommendation.
The single biggest cause of wrong home generator sizing is confusing these two numbers. Understanding the difference is essential for correct sizing.
The continuous power an appliance needs while operating. A refrigerator uses roughly 700 W running. This is the base load your generator must supply steadily.
The short burst of extra power a motor needs in its first 2–3 seconds. A well pump can draw 4,500 W to start even though it runs at 1,500 W. Central AC can demand 3–4× its running load at startup.
Total starting load = sum of all running watts + the single highest starting surge. You add only the one largest surge because home appliances rarely all start at the exact same moment.
A generator that runs your lights and fridge all day can still fail the instant a central air conditioner's compressor starts. The generator trips and you lose power exactly when you need it most.
Refrigerator: 3× running. Well pump: 3–4×. Central AC: 3–4×. Window AC: 2×. Furnace fan: 2–3×. Sump pump: 2×. Always check the nameplate for exact values.
Refrigerator: 700W run / 2,200W start
Well pump (1 HP): 1,500W / 4,500W
Central AC (3 ton): 3,500W / 6,000–7,000W
Electric water heater: 4,000–4,500W (no surge)
Microwave: 1,000–1,500W (no surge)
Most sizing problems come from a small number of recurring assumptions. Avoiding these errors helps prevent both undersized equipment and unnecessary excess capacity.
A generator that runs your lights and fridge all day can still fail the instant a central air conditioner's compressor starts. Count the largest surge.
For a single-phase home, kW ≈ kVA, because the power factor is close to 1.0. A "10 kW house" needs a 10 kVA unit — not a larger one sized by a three-phase conversion rule.
A diesel generator run below about 30% load suffers wet stacking — carbon buildup that raises fuel use and wears the engine faster. Correct sizing saves money on both purchase and operation.
A 60 Hz US unit is not automatically correct for a 50 Hz country. Confirm the unit matches your local supply before ordering. Our calculator supports both frequencies.
Adding an extra 10–15% now is far cheaper than replacing the unit when you add a freezer, a pump, or another air conditioner later. Plan for future growth.
Final generator selection should be checked against your complete load schedule, motor-starting sequence, power factor, site conditions and duty rating before equipment is ordered. Our engineers are available to review your specific requirements at no charge.
Use your calculated generator size as the basis for a tailored quotation from ShanHua Power. Our engineers will confirm the specification and provide a complete solution with no obligation — free sizing consultation included.
A: For essential backup — refrigerator, lights, well or sump pump, furnace fan — you typically need 3–5 kW. For comfort coverage that includes air conditioning, plan on 7–15 kW. A whole-home setup with central AC and electric appliances can require 15–30+ kW. Run your appliance list through the calculator for a precise answer.
A: A typical home needs 8–22 kW depending on size and air conditioning. A smaller home with essential loads runs on 5–10 kW; a larger home with central AC and electric appliances needs 20–30 kW. The exact figure depends on your appliance list, not just square footage.
A: Yes. A diesel generator sized to your load will power a house reliably, with the advantage of on-site fuel storage and long runtime — no natural gas line required. This makes diesel the standard choice for off-grid, rural and outage-prone locations.
A: Running watts are what an appliance consumes continuously. Starting watts are the extra burst needed for a few seconds when motors start — often 3 to 7 times the running load. The generator must handle the starting watts of its largest motor, or it will trip when that appliance switches on.
A: It depends on tank size and load. A diesel set at typical home load can run for many hours on a standard tank, and it can be refueled on-site for continuous operation. The calculator above provides runtime estimates based on your calculated load.
A: Almost all homes run on single-phase power. You only need a three-phase generator for a very large residence or if you are also powering commercial equipment. Our calculator defaults to single-phase for home use and confirms this in the result.
A: You pay more to buy it, and running it under light load causes wet stacking, higher fuel consumption per kWh, and faster engine wear. Correct sizing saves money on both purchase and operation.
A: Yes. We offer OEM/ODM customization across our range. If your calculated size, voltage, frequency or enclosure does not match a standard model, our engineering team will configure the unit to your specification.
