2.5 mm² to AWG
2.5 mm² is the single most stocked cable size in European auto-electrical and marine shops — the default for every branch circuit that outgrows 1.5 mm². Its AWG twin is the oddball: 13 AWG (2.62 mm²) sits between the common even sizes 14 and 12 AWG and is rarely sold in North America. That is why 2.5 mm² datasheets list "13 AWG equivalent" while US shopping lists round to 12 AWG for the same job. At 20 A ampacity, 2.5 mm² covers combined lighting trunks, fridge branches, and heavy accessory circuits.
All values on this page assume copper conductors at 20°C ambient. Aluminum has ~60% higher resistance for the same cross-section and is generally not recommended for low-voltage DC.
Calculate for your specific cable run
The tables below assume 13 AWG (2.5 mm²) copper. Use the calculator to confirm this gauge is correct for your exact load and length, or get a different gauge recommendation if needed.
= 60W
= 16.4 ft (one way, round-trip calculated automatically)
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Download Cable for iOS13 AWG Voltage Drop at 12V DC
Round-trip voltage drop for 13 AWG (2.5 mm²) copper wire at 20°C ambient. Cells highlighted in yellow exceed the 3% target; red cells exceed 5% and are not recommended.
| Current | 1 m / 3 ft | 2 m / 7 ft | 3 m / 10 ft | 5 m / 16 ft | 7 m / 23 ft |
|---|---|---|---|---|---|
| 3 A | 0.043 V (0.36%) | 0.086 V (0.71%) | 0.13 V (1.07%) | 0.21 V (1.79%) | 0.30 V (2.50%) |
| 5 A | 0.071 V (0.59%) | 0.14 V (1.19%) | 0.21 V (1.79%) | 0.36 V (2.97%) | 0.50 V (4.17%) |
| 10 A | 0.14 V (1.19%) | 0.29 V (2.38%) | 0.43 V (3.57%) | 0.71 V (5.95%) | 1.00 V (8.33%) |
| 15 A | 0.21 V (1.79%) | 0.43 V (3.57%) | 0.64 V (5.35%) | 1.07 V (8.92%) | 1.50 V (12.49%) |
| 20 A | 0.29 V (2.38%) | 0.57 V (4.76%) | 0.86 V (7.14%) | 1.43 V (11.90%) | 2.00 V (16.66%) |
13 AWG Voltage Drop at 24V DC
Round-trip voltage drop for 13 AWG (2.5 mm²) copper wire at 20°C ambient. Cells highlighted in yellow exceed the 3% target; red cells exceed 5% and are not recommended.
| Current | 1 m / 3 ft | 2 m / 7 ft | 3 m / 10 ft | 5 m / 16 ft | 7 m / 23 ft |
|---|---|---|---|---|---|
| 3 A | 0.043 V (0.18%) | 0.086 V (0.36%) | 0.13 V (0.54%) | 0.21 V (0.89%) | 0.30 V (1.25%) |
| 5 A | 0.071 V (0.30%) | 0.14 V (0.59%) | 0.21 V (0.89%) | 0.36 V (1.49%) | 0.50 V (2.08%) |
| 10 A | 0.14 V (0.59%) | 0.29 V (1.19%) | 0.43 V (1.79%) | 0.71 V (2.97%) | 1.00 V (4.17%) |
| 15 A | 0.21 V (0.89%) | 0.43 V (1.79%) | 0.64 V (2.68%) | 1.07 V (4.46%) | 1.50 V (6.25%) |
| 20 A | 0.29 V (1.19%) | 0.57 V (2.38%) | 0.86 V (3.57%) | 1.43 V (5.95%) | 2.00 V (8.33%) |
What is 13 AWG (2.5 mm²) used for?
Camper / RV applications
- Combined lighting trunk lines feeding several zones (8–15 A)
- Compressor fridge branches up to 10 A continuous
- 12V distribution to USB-C PD outlets (100 W chargers pull ~9 A)
- Water pumps up to 10 A continuous with inrush headroom
- Diesel heater feeds (Autoterm, Webasto — 10–15 A glow-plug phase)
Boat / marine applications
- Cabin lighting trunks and spreader lights
- Freshwater and washdown pumps up to 10 A
- Instrument buses combining plotter, VHF, and AIS
- Fridge branch circuits on daysailers
- Windlass control (not feed) circuits
Off-grid / solar applications
- Lighting and outlet branches in tiny homes and cabins
- PV string wiring for single panels up to 20 A
- Shed sub-feeds for lighting plus router/monitoring loads
- Fan and ventilation circuits
When to step up
- Continuous current above 16 A — within 20% of ampacity
- Cable runs longer than 5 m at 12V with currents above 10 A
- Motor loads with inrush above 25 A (pumps, blowers) — use 4 mm²
- Any feed you might later extend: 4 mm² costs cents more per metre
Fuse size for 13 AWG (2.5 mm²)
The fuse must protect the wire, not the load. For 13 AWG copper (2.5 mm²) the maximum fuse rating is 20 A. Below this ceiling, size the fuse at 125% of your continuous load current and round up to the next standard fuse size.
| Continuous Load | 125% Calculation | Recommended Fuse | Fuse Type |
|---|---|---|---|
| 2 A | 2.5 A | 5 A | Blade (ATC) |
| 5 A | 6.25 A | 7.5 A | Blade (ATC) |
| 8 A | 10 A | 10 A | Blade (ATC) |
| 10 A | 12.5 A | 15 A | Blade (ATC) |
| 17 A | 21.25 A | 20 A | Blade (ATC) |
Related conversions
Frequently Asked Questions
What is 2.5 mm² in AWG?
2.5 mm² converts to 13 AWG (2.62 mm² precise) — closer to 13 AWG than to 14 AWG (2.08 mm²). Because 13 AWG is rarely sold in North America, the practical substitutes are 12 AWG (3.31 mm², safe in both directions) or 14 AWG where the load stays under 15 A.
How many amps can 2.5 mm² wire handle?
2.5 mm² copper cable is rated for 20 A continuous at 20°C in chassis wiring. It is the standard European size for branch circuits that outgrow 1.5 mm²: combined lighting trunks, fridge branches, water pumps, and diesel heaters.
Is 2.5 mm² enough for a 12V fridge?
Yes for typical 12V compressor fridges (Dometic CRX, Vitrifrigo) drawing 4–7 A continuous with ~15 A inrush. Keep the run under 6 m at 12V for under 3% voltage drop. For chest fridges above 10 A continuous or runs beyond 8 m, use 4 mm².
What size fuse for 2.5 mm² cable?
Maximum 20 A. Size the fuse at 125% of the continuous load and round up: a 7 A fridge takes a 10 A fuse, a 12 A heater feed takes a 15 A fuse. Use standard ATC/ATO blade fuses at this current level.
Should I use 2.5 mm² or 4 mm² for my camper build?
Use 2.5 mm² for branch circuits up to 16 A continuous and runs under 5 m. Use 4 mm² for anything with motor inrush (pumps, blowers), runs beyond 5 m, or circuits you may extend later. Many builders standardize on 2.5 mm² for branches and 4–6 mm² for feeds — two spools cover the whole interior.