12V Fuse Size Calculator
Enter watts or amps and get the recommended fuse rating, fuse type, and the wire gauge it protects -- for 12V, 24V, and 48V DC systems in RVs, boats, campers, and off-grid solar.
12V Fuse Size Calculator
= 60W
= 16.4 ft (one way, round-trip calculated automatically)
Advanced Settings
Result
Fuse Size
Materials
- Battery cable2.5 mm² · 2 × 6 m
- Fuse7.5 A · Blade (ATC/ATO) · × 1
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Download Cable for iOSWhat Size Fuse for Each Wire Gauge? (12V DC)
A fuse protects the wire, so it must always be rated at or below the wire ampacity. This table shows the maximum fuse size for each common wire gauge, plus the fuse type used at that current. Need to size the wire itself? Use the wire gauge calculator.
| Wire Gauge | Max Fuse | Fuse Type | Common Loads |
|---|---|---|---|
| 18 AWG / 0.75mm² | 7A | Blade (ATC) | LED strips, sensors |
| 16 AWG / 1.0mm² | 10A | Blade (ATC) | Interior lights, small fans |
| 14 AWG / 1.5mm² | 15A | Blade (ATC) | Lights, USB outlets, vent fans |
| 12 AWG / 4.0mm² | 25A | Blade (ATC) | Water pumps, heater fans, fridges |
| 10 AWG / 6.0mm² | 35A | MAXI Blade | Compressor fridges, large fans |
| 8 AWG / 10.0mm² | 50A | MAXI Blade | Sub-panels, DC-DC chargers |
| 6 AWG / 16.0mm² | 65A | ANL | Small inverters, shore power chargers |
| 4 AWG / 25.0mm² | 85A | ANL | Battery interconnects, medium inverters |
| 2 AWG / 35.0mm² | 110A | ANL | Large battery banks, high-current runs |
| 1/0 AWG / 50.0mm² | 135A | Class T | Main battery fuse, large inverters |
| 2/0 AWG / 120.0mm² | 235A | Class T | High-power inverters, bus bars |
| 3/0 AWG / 150.0mm² | 285A | Class T | Bow thrusters, windlasses |
| 4/0 AWG / 185.0mm² | 330A | Class T | High-power marine loads |
Frequently Asked Questions
How to calculate fuse size for 12V?
Divide the load watts by the voltage to get amps, multiply by 1.25 for the continuous-load safety margin, then round up to the next standard fuse size. Example: a 60W load on 12V draws 5A, so the minimum fuse is 7.5A. The fuse rating must never exceed the wire ampacity. The calculator above does this automatically.
What size fuse do I need?
Size the fuse at 125% of the continuous load current, rounded up to the nearest standard fuse size, and never larger than the wire it protects. Enter your watts or amps above and the calculator returns the recommended fuse rating and the matching fuse type.
What size fuse for 14 gauge wire 12V?
14 gauge wire (1.5mm²) is rated for up to 15 amps. Use a fuse rated at or below 15A -- typically a 10A or 15A blade fuse depending on your actual load. Never install a fuse larger than the wire can safely carry.
What size fuse for 12 gauge wire 12V?
12 gauge wire (4.0mm²) is rated for up to 25 amps. A 20A or 25A blade fuse is appropriate. Choose the fuse from your actual load current (125% of load, rounded up), making sure it does not exceed the 25A wire rating.
What size fuse for 16 gauge wire 12V?
16 gauge wire (1.0mm²) is rated for up to 10 amps. Use a fuse rated at or below 10A -- typically a 5A or 10A blade fuse based on the connected load.
Is a fuse sized by the wire or the load?
The fuse protects the wire, not the load device. Size it from the continuous load current (125%, rounded up), but it must never exceed the ampacity of the wire it sits on. If the load is small but the wire is thin, the wire ampacity sets the ceiling.
Where should the fuse be placed?
As close to the battery positive terminal as possible -- ideally within 18cm (7 inches). The wire between the battery and the fuse is unprotected; if it shorts to the chassis, there is nothing to prevent a fire. This is the single most important fuse placement rule in any DC system.
Which fuse type should I use -- blade, MAXI, ANL, or Class T?
Blade fuses (ATC/ATO) cover circuits up to ~30A, MAXI blade fuses up to ~60A, ANL bolt-down fuses up to ~200A, and Class T fuses (fast-acting, high interrupt rating) are used for inverters and main battery protection up to ~400A. The calculator recommends the appropriate type for your current.
What size main fuse for a 12V battery?
The main battery fuse is sized from the total maximum load of all circuits combined. For a typical camper or boat drawing 100-200A total, a 150-200A ANL or Class T fuse is common. Each individual circuit downstream also needs its own smaller fuse matched to its wire gauge.
How Fuse Sizing Works in DC Systems
A fuse is a deliberate weak link: it melts and breaks the circuit before the wire downstream can overheat and start a fire. That is why a fuse is sized to protect the wire, not the device at the end of it.
The 125% Rule
Standard practice is to rate the fuse at 125% of the continuous load current, then round up to the next standard size. The 25% headroom stops nuisance trips from normal current swings while still blowing well before the wire is in danger.
The Fuse Must Never Exceed the Wire
Whatever the load asks for, the fuse rating must stay at or below the ampacity of the wire it sits on. A 30A fuse on 16 AWG wire (rated 10A) is dangerous -- the wire can melt while the fuse happily passes current. When the calculated fuse approaches the wire limit, step up a wire gauge with the wire gauge calculator.
Placement
Mount the fuse as close to the battery positive terminal as possible. The short length of wire between the battery and the fuse is unprotected, so keep it under 18cm (7 inches) wherever you can.
Related Resources
Wire Gauge Calculator
Size the wire in AWG or mm² from current, length, and voltage drop. The companion to fuse sizing.
12V Fuse Sizing & Placement Guide
The full guide: the 125% rule, fuse types (ANL, MIDI, blade, Class T), and battery placement rules.
Fuse Sizing Cheat Sheet
Printable quick-reference card with fuse sizes for 20+ common devices in campers and boats.
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