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Fuse Size Calculator

Converts an appliance wattage into the current it draws and recommends the next standard fuse rating above it.

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Enter your figures and press Calculate.
In short Fuse Size Calculator is a free online tool on inputtesthub.com that converts an appliance wattage into the current it draws and recommends the next standard fuse rating above it. 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 Fuse 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 Fuse Size Calculator

The Fuse Size Calculator converts an appliance wattage into the current it draws and recommends the next standard fuse rating above it. 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

  • Choosing between a 3 A and a 13 A plug fuse.
  • Checking the current an appliance draws.
  • Sizing a circuit fuse for a fixed appliance.

Details

Up to ~700 W at 230 V3 A fuse
Above that13 A fuse
Margin applied25%
Standard ratings3, 5, 10, 13, 16, 20, 32 A

The maths behind it

This tool uses Current = watts ÷ volts. Add 25% margin, then take the next standard fuse rating above that. Every intermediate value is shown on screen, so the result can be checked by hand.

A fuse protects the cable, not the appliance. Fitting a larger fuse because a smaller one keeps blowing removes the protection — repeated blowing means a fault. Anything beyond replacing a plug fuse is work for a qualified electrician.

Frequently asked questions

Does the Fuse Size Calculator cost anything?
There is no cost and no cap. The Fuse Size Calculator is not a demo of a paid product, so nothing is held back or watermarked.
Is what I paste into the Fuse Size Calculator stored?
No. The Fuse Size Calculator runs entirely in your browser using JavaScript. Your input never reaches inputtesthub.com or any third party — open your browser's Network tab while you use it and you will see no request go out.
What formula does the Fuse Size Calculator use?
It uses Current = watts ÷ volts. Add 25% margin, then take the next standard fuse rating above that. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What do people use the Fuse Size Calculator for most?
Typical uses: choosing between a 3 A and a 13 A plug fuse. Checking the current an appliance draws. Sizing a circuit fuse for a fixed appliance. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Any caveats I should know about?
A fuse protects the cable, not the appliance. Fitting a larger fuse because a smaller one keeps blowing removes the protection — repeated blowing means a fault. Anything beyond replacing a plug fuse is work for a qualified electrician.
What are the reference figures here?
Up to ~700 W at 230 V is 3 A fuse. Above that is 13 A fuse. Margin 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.

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