25 mm² to AWG
4 AWG is where DC wiring stops being light branch circuits and starts being serious power transmission. It is the default for battery bank interconnects, feeds to medium inverters (1000–1500 W class at 12V), and the main distribution between battery and fuse panel. At this gauge, friction-fit terminals stop being acceptable — every 4 AWG termination needs a hexagonal crimp die, heat-shrink, and ideally a torque-checked stud connection.
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 4 AWG (25 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 iOS4 AWG Voltage Drop at 12V DC
Round-trip voltage drop for 4 AWG (25 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 | 3 m / 10 ft | 5 m / 16 ft | 10 m / 33 ft | 20 m / 66 ft |
|---|---|---|---|---|---|
| 20 A | 0.029 V (0.24%) | 0.086 V (0.71%) | 0.14 V (1.19%) | 0.29 V (2.38%) | 0.57 V (4.76%) |
| 40 A | 0.057 V (0.48%) | 0.17 V (1.43%) | 0.29 V (2.38%) | 0.57 V (4.76%) | 1.14 V (9.52%) |
| 60 A | 0.086 V (0.71%) | 0.26 V (2.14%) | 0.43 V (3.57%) | 0.86 V (7.14%) | 1.71 V (14.28%) |
| 80 A | 0.11 V (0.95%) | 0.34 V (2.86%) | 0.57 V (4.76%) | 1.14 V (9.52%) | 2.28 V (19.04%) |
| 100 A | 0.14 V (1.19%) | 0.43 V (3.57%) | 0.71 V (5.95%) | 1.43 V (11.90%) | 2.86 V (23.80%) |
4 AWG Voltage Drop at 24V DC
Round-trip voltage drop for 4 AWG (25 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 | 3 m / 10 ft | 5 m / 16 ft | 10 m / 33 ft | 20 m / 66 ft |
|---|---|---|---|---|---|
| 20 A | 0.029 V (0.12%) | 0.086 V (0.36%) | 0.14 V (0.60%) | 0.29 V (1.19%) | 0.57 V (2.38%) |
| 40 A | 0.057 V (0.24%) | 0.17 V (0.71%) | 0.29 V (1.19%) | 0.57 V (2.38%) | 1.14 V (4.76%) |
| 60 A | 0.086 V (0.36%) | 0.26 V (1.07%) | 0.43 V (1.79%) | 0.86 V (3.57%) | 1.71 V (7.14%) |
| 80 A | 0.11 V (0.48%) | 0.34 V (1.43%) | 0.57 V (2.38%) | 1.14 V (4.76%) | 2.28 V (9.52%) |
| 100 A | 0.14 V (0.60%) | 0.43 V (1.79%) | 0.71 V (2.97%) | 1.43 V (5.95%) | 2.86 V (11.90%) |
What is 4 AWG (25 mm²) used for?
Camper / RV applications
- Battery bank interconnects (2–4 batteries in parallel)
- Inverter feeds up to 1500 W at 12V (~125 A)
- Main battery-to-fuse-panel distribution cable
- Large MPPT to battery on 60–80 A controllers
- B2B (DC-DC) chargers above 40 A
Boat / marine applications
- House-bank battery interconnects
- Windlass feed on medium-size boats
- Inverter feeds for refrigeration and AC outlets
- Alternator-to-battery on systems with high-output alternators
- Bow thruster on smaller boats (under 4 kW)
Off-grid / solar applications
- Battery bank interconnects (lithium parallel banks)
- 1500–2000 W inverter feeds at 12V or 3000 W at 24V
- Main battery cabinet wiring
- Class T or ANL fuse to bus bar feeds
When to step up
- Inverter loads above 1500 W at 12V — needs 2 AWG or 1/0
- Battery banks above 400 Ah parallel — heavier interconnect cables
- Continuous current above 70 A — close to ampacity
- Cable runs longer than 4 m at 12V with currents above 60 A
Fuse size for 4 AWG (25 mm²)
The fuse must protect the wire, not the load. For 4 AWG copper (25 mm²) the maximum fuse rating is 85 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 |
|---|---|---|---|
| 10 A | 12.5 A | 15 A | Blade (ATC) |
| 15 A | 18.75 A | 20 A | Blade (ATC) |
| 20 A | 25 A | 25 A | Blade (ATC) |
| 55 A | 68.75 A | 70 A | ANL |
| 80 A | 100 A | 100 A | ANL |
Related conversions
Frequently Asked Questions
What is 25 mm² in AWG?
25 mm² is the metric pairing for 4 AWG in international cable standards. The precise AWG value of 25 mm² is between 3 AWG (26.7 mm²) and 4 AWG (21.15 mm²) — closer to 3 AWG. In practice, 25 mm² and 4 AWG are matched in cable spec tables and used interchangeably.
How many amps can 25 mm² wire handle?
25 mm² copper cable is rated for 85 A continuous at 20°C in chassis wiring — the same ampacity as 4 AWG. For high-temperature engine compartments or bundled cable runs, derate by 10–20%.
Is 25 mm² enough for an inverter?
For inverters up to 1000 W at 12V (~85 A continuous), 25 mm² works at the limit. For 1500 W or larger inverters at 12V, step up to 35 mm² (2 AWG) or 50 mm² (1 AWG). At 24V, 25 mm² handles inverters up to 2000 W comfortably.
What size fuse for 25 mm² cable?
Maximum fuse for 25 mm² is 85 A. Below that ceiling, size at 125% of continuous load: 60 A load → 80 A fuse, 70 A load → 100 A (or step up cable size). Use ANL or Class T fuses at this current level — blade fuses are not appropriate.