DC Fuse Sizing Calculator
Fuse rating from continuous load with headroom factor, snapped to standard sizes and checked against your wire's capacity.
A fuse protects the WIRING, not the device โ electronics die far faster than any fuse blows. Use slow-blow types for motors and capacitive inrush, fast types for semiconductors. DC arcs are harder to break than AC: check the fuse's DC voltage rating (a 250 VAC glass fuse may only be rated 32 VDC). In vehicles, put the fuse within ~150 mm of the battery terminal.
DC Fuse Sizing Calculator computes the standard fuse rating for a load, checked against the wire it must protect โ free, instant and private in your browser. Automotive and solar wirers, battery-system builders and bench-supply protectors use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About DC Fuse Sizing Calculator
DC Fuse Sizing Calculator computes the standard fuse rating for a load, checked against the wire it must protect using the standard engineering relation: fuse โฅ 1.25โ2 ร continuous current (duty-dependent), rounded up to standard, but โค wire ampacity. Worked live: an 18 A continuous load ร 1.25 = 22.5 A โ 25 A standard fuse, which AWG 10 wiring supports. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side โ nothing you type leaves your device.
How to use DC Fuse Sizing Calculator
- 1Enter your values โ the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use DC Fuse Sizing Calculator?
- โImplements the real formula โ fuse โฅ 1.25โ2 ร continuous current (duty-dependent), rounded up to standard, but โค wire ampacity โ with the substitution shown, not a black box
- โBuilt for automotive and solar wirers, battery-system builders and bench-supply protectors
- โCopy result and permalink buttons โ share the exact calculation in a README, forum answer or design review
- โ100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate dc fuse sizing?+
The standard fuse rating for a load, checked against the wire it must protect follows fuse โฅ 1.25โ2 ร continuous current (duty-dependent), rounded up to standard, but โค wire ampacity. For example, an 18 A continuous load ร 1.25 = 22.5 A โ 25 A standard fuse, which AWG 10 wiring supports. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Does the fuse protect my device?+
No โ fuses protect the WIRING from fire. Semiconductors die in microseconds; fuses open in milliseconds to seconds. Choose the fuse for the cable's ampacity and route; protect electronics with their own current limiting, TVS or crowbar circuits.
Why does my correctly-sized fuse keep blowing at switch-on?+
Inrush: motors, capacitive inputs and incandescent loads draw 5โ10ร rated current briefly. Use a time-delay (slow-blow) fuse of the same rating rather than a bigger fast fuse โ the bigger fast fuse quietly removes your wire protection.
Is the DC Fuse Sizing Calculator free and private?+
Yes โ completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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