InputTestHub

Generator Size Calculator

Sizes a generator in kVA from your total running watts and starting surge, applying headroom and power factor.

Calculators Nothing uploaded No sign-up Free, unlimited
Calculators tool
Enter your figures and press Calculate.
In short Generator Size Calculator is a free online tool on inputtesthub.com that sizes a generator in kVA from your total running watts and starting surge, applying headroom and power factor. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Generator Size Calculator

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Generator Size Calculator

The Generator Size Calculator sizes a generator in kVA from your total running watts and starting surge, applying headroom and power factor. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Sizing a backup generator for a house.
  • Checking whether an existing generator can start a water pump.
  • Comparing kVA ratings between models.

Details

1 kVA at pf 0.8800 watts
Motor surge2–3× running current
Headroom applied25%
Best continuous load≈ 80% of rating

The maths behind it

This tool uses Governing watts = the larger of (running × 1.25) and the surge figure. kVA = watts ÷ 1,000 ÷ power factor. Every intermediate value is shown on screen, so the result can be checked by hand.

Surge is what sizes a generator, not running load. A fridge, water pump or AC draws two to three times its running current at start-up, and a generator that cannot supply it will stall even though the steady load is well within range. Never run a generator indoors or in a partly enclosed space — the carbon monoxide risk is lethal.

Frequently asked questions

Are there any usage caps on the Generator Size Calculator?
No charge and no sign-up. There is no free tier to run out of because there is no paid tier — inputtesthub.com is funded by advertising rather than by metering the tool.
Does anything I enter leave my computer?
No. The Generator Size Calculator runs entirely in your browser using JavaScript. Nothing is transmitted, logged or stored, which you can verify yourself in the Network tab of your browser's developer tools.
Can I check the maths myself?
It uses Governing watts = the larger of (running × 1.25) and the surge figure. kVA = watts ÷ 1,000 ÷ power factor. The full working is printed under the result, so you can follow every step rather than trusting a black box.
When would I actually need the Generator Size Calculator?
In practice it gets used for three things: sizing a backup generator for a house. Checking whether an existing generator can start a water pump. Comparing kVA ratings between models. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there a catch?
Surge is what sizes a generator, not running load. A fridge, water pump or AC draws two to three times its running current at start-up, and a generator that cannot supply it will stall even though the steady load is well within range. Never run a generator indoors or in a partly enclosed space — the carbon monoxide risk is lethal.
What figures does the Generator Size Calculator work from?
1 kVA at pf 0.8 is 800 watts. Motor surge is 2–3× running current. Headroom applied is 25%. These are printed on the page itself, so you do not have to take them on trust.
How precise is the result?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

Related calculators tools

All 382
01

Loan Calculator

Works out the monthly payment, total interest and full repayment schedule for any loan from…

02

EMI Calculator

Calculates your Equated Monthly Instalment with a full principal-versus-interest breakdown and…

03

Mortgage Calculator

Estimates a full monthly housing payment including principal, interest, property tax…

04

Car Loan Calculator

Calculates a car finance payment from the price, deposit, trade-in, interest rate and term…

05

Personal Loan Calculator

Works out instalments and total cost for an unsecured personal loan, including any processing…

09

SIP Calculator

Projects the maturity value of a monthly Systematic Investment Plan, showing invested amount…