18 AWG to mm²
18 AWG (0.75 mm²) is the thinnest standard cable still considered "wiring" in DC systems — below it, you are into signal-wire and pre-tinned BMS-cable territory. It handles small loads under 7 A: indicator LEDs, low-power dome lights, sensor feeds, and the trigger sides of relays. In stocked metric markets, 0.75 mm² is the smallest cable typically sold off the spool, available alongside 1.0 mm² and 1.5 mm². Anything below 0.75 mm² is usually multi-conductor sheathed cable for trailer plugs or sensor harnesses.
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 18 AWG (0.75 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 iOS18 AWG Voltage Drop at 12V DC
Round-trip voltage drop for 18 AWG (0.75 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 |
|---|---|---|---|---|---|
| 1 A | 0.046 V (0.39%) | 0.093 V (0.77%) | 0.14 V (1.16%) | 0.23 V (1.93%) | 0.32 V (2.71%) |
| 2 A | 0.093 V (0.77%) | 0.19 V (1.55%) | 0.28 V (2.32%) | 0.46 V (3.87%) | 0.65 V (5.41%) |
| 3 A | 0.14 V (1.16%) | 0.28 V (2.32%) | 0.42 V (3.48%) | 0.70 V (5.80%) | 0.97 V (8.12%) |
| 5 A | 0.23 V (1.93%) | 0.46 V (3.87%) | 0.70 V (5.80%) | 1.16 V (9.67%) | 1.62 V (13.53%) |
| 7 A | 0.32 V (2.71%) | 0.65 V (5.41%) | 0.97 V (8.12%) | 1.62 V (13.53%) | 2.27 V (18.95%) |
18 AWG Voltage Drop at 24V DC
Round-trip voltage drop for 18 AWG (0.75 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 |
|---|---|---|---|---|---|
| 1 A | 0.046 V (0.19%) | 0.093 V (0.39%) | 0.14 V (0.58%) | 0.23 V (0.97%) | 0.32 V (1.35%) |
| 2 A | 0.093 V (0.39%) | 0.19 V (0.77%) | 0.28 V (1.16%) | 0.46 V (1.93%) | 0.65 V (2.71%) |
| 3 A | 0.14 V (0.58%) | 0.28 V (1.16%) | 0.42 V (1.74%) | 0.70 V (2.90%) | 0.97 V (4.06%) |
| 5 A | 0.23 V (0.97%) | 0.46 V (1.93%) | 0.70 V (2.90%) | 1.16 V (4.83%) | 1.62 V (6.77%) |
| 7 A | 0.32 V (1.35%) | 0.65 V (2.71%) | 0.97 V (4.06%) | 1.62 V (6.77%) | 2.27 V (9.47%) |
What is 18 AWG (0.75 mm²) used for?
Camper / RV applications
- Indicator LEDs on the control panel (under 200 mA)
- Reading lights with single LED chips (1–3 A)
- Relay coil trigger wires (50–200 mA)
- Switch panel feeds (combined under 5 A)
- Temperature and tank-level sensor wires
Boat / marine applications
- Indicator lights and panel illumination
- NMEA 2000 power taps (drop cables)
- Switch panel feeds for chartplotter and instruments
- Bilge alarm and sensor wiring
- Stereo speaker wires for low-power systems
Off-grid / solar applications
- BMS communication and sense leads
- Sensor wiring for temperature and voltage monitors
- Remote display data cables
- Trigger wires for high-current contactors
- Low-side relay coil wiring
When to step up
- Continuous current above 5 A — within 30% of ampacity
- Cable runs longer than 5 m at 12V with currents above 3 A
- Any load with inductive surge (relay coils, small motors)
- When in doubt — stepping up to 1.5 mm² costs almost nothing on short runs
Fuse size for 18 AWG (0.75 mm²)
The fuse must protect the wire, not the load. For 18 AWG copper (0.75 mm²) the maximum fuse rating is 7 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 | 7.5 A | Blade (ATC) |
| 10 A | 12.5 A | 7.5 A | Blade (ATC) |
Related conversions
Frequently Asked Questions
What is 18 AWG in mm²?
18 AWG is precisely 0.823 mm² by the IEC formula. In standard metric cable, 18 AWG is sold as 0.75 mm² — the closest stocked size below the precise value. The VoltPlan calculator uses 0.75 mm² (7 A ampacity) as the metric equivalent of 18 AWG.
How many amps can 18 AWG handle?
18 AWG copper (0.75 mm²) is rated for 7 A continuous at 20°C in chassis wiring — enough for indicator LEDs, dome lights, sensor feeds, and relay coils. For anything above 5 A continuous, step up to 16 AWG (1 mm²) or 14 AWG (1.5 mm²).
What size fuse for 18 AWG wire?
Use a 5 A or 7.5 A blade fuse to protect 18 AWG (0.75 mm²) on 12V. Never exceed 7 A on this gauge. For sense leads and panel feeds under 1 A, a 3 A or 5 A fuse is more practical than the theoretical 1.25× sizing.
Can I use 18 AWG for trailer lights?
Only for indicator and marker lights at low current. Brake lights, turn signals, and any halogen-style lighting need 16 AWG (1 mm²) minimum, and LED brake lights on long trailers should use 14 AWG to keep voltage drop under 3%. 18 AWG is for the 7-pin trailer plug signal lines, not the main lighting feeds.
Is 18 AWG enough for an LED reading light?
Yes for single-LED reading lights (1–3 A). For multi-LED puck arrays or dimmable lights with 5+ A draw, use 16 AWG (1 mm²) or 14 AWG (1.5 mm²). The voltage drop on 18 AWG above 5 A causes visible dimming on cable runs over 3 m.