Enter your Load Current, Circuit Voltage, Circuit Type, and wire details like Wire Size (AWG) and Number of Bundled Wires to get your Recommended Fuse Size — plus the Minimum and Maximum Fuse Size and Safety Margin so you know exactly how much headroom you're working with.
Recommended Fuse Size
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Minimum Fuse Size
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Maximum Fuse Size
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Safety Margin
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Use a branch circuit fuse for individual loads like lights or radios. Use a feeder circuit fuse for main power lines that supply multiple branch circuits or devices.
Motors draw much higher current during startup (inrush current) than their normal operating current. The fuse must handle this temporary surge without blowing.
Multiple wires bundled together generate more heat and reduce current carrying capacity. More bundled wires require lower fuse ratings to prevent overheating.
Minimum fuse size protects the load from damage. Maximum fuse size protects the wire from overheating. Your fuse should be between these values.
Always round up to the next available standard fuse size. Never use a fuse smaller than the calculated minimum or larger than the calculated maximum.
Engine rooms have higher ambient temperatures, which reduces wire current capacity and may require derating the fuse size for safety.
This calculator is designed for DC circuits (12V, 24V, 32V). AC circuits have different safety requirements and should follow AC electrical codes.
Too small: fuse blows unnecessarily during normal operation. Too large: won't protect wire from overheating and fire risk, potentially causing dangerous conditions.