Fuse Size Calculator
Enter your circuit current or calculate current from watts and voltage to estimate a recommended fuse rating for your electrical load.
Enter Circuit Details
Recommended Fuse Size
Your Result Appears Here
Enter the circuit information and select “Calculate Fuse Size” to see the estimated fuse rating.
What Is a Fuse Size Calculator?
A fuse size calculator estimates an appropriate fuse rating from the normal operating current of an electrical load. It can also calculate current from power and voltage when amperage is not already known.
The calculator applies your selected sizing factor and then finds the next available rating from a list of commonly used fuse sizes. The result is intended as a useful starting point, not as a replacement for manufacturer specifications or applicable electrical requirements.
How the Fuse Size Calculator Works
Enter the Load
Provide the normal current directly or enter power and voltage so the calculator can estimate amperage.
Choose a Factor
Select the sizing multiplier you want applied to the calculated operating current.
Get the Fuse Rating
The tool calculates the minimum value and displays the next standard fuse rating.
Fuse Size Formula
When the normal operating current is known, this calculator uses the following basic relationship.
Fuse Size = Load Current × Sizing Factor
For example, a load drawing 20 amps with a 125% multiplier produces a calculated value of 25 amps. If 25 A is available as a standard fuse rating, the calculator displays 25 A.
Current From Watts and Voltage
When power and voltage are entered, load current is estimated using the relationship below.
Current = Power ÷ (Voltage × Efficiency)
Why Correct Fuse Sizing Matters
A fuse is intended to interrupt a circuit when current becomes excessive. Choosing a fuse that is too small may cause unwanted operation during normal use, while a fuse that is too large may not provide suitable protection for the wiring or equipment.
Actual fuse selection can also depend on conductor capacity, operating temperature, startup current, equipment instructions, voltage rating, AC or DC operation and the time-current characteristics of the fuse.
Fuse Size Calculator FAQs
Multiply the normal load current by the appropriate sizing factor. Then compare that result with available standard fuse ratings while ensuring the fuse does not exceed the safe rating of the protected wiring or equipment.
Yes. Select Power & Voltage, enter watts, voltage and efficiency, and the calculator will estimate current before calculating the fuse size.
A multiplier above normal current can be useful in some applications, but the correct factor depends on the equipment and circuit. Always verify the final rating against the applicable requirements.
No. A fuse that is too large can allow excessive current to flow through wiring or equipment. The fuse rating should be appropriate for the protected circuit.
The tool can provide a basic current-based estimate, but an actual fuse must also have voltage and interrupt ratings suitable for the particular DC circuit.