What wire gauge do I need for 12V in a camper van?

This depends on the current and cable length. For light circuits (lighting, USB) 1.5-2.5 mm² is sufficient. For heavier consumers like a fridge or water pump, use 4-6 mm². For an inverter you need 25-50 mm². Always use a calculator for your specific situation.

How much voltage drop is acceptable in a camper van?

For most 12V circuits, a maximum of 3% is recommended (0.36V at 12V). For sensitive electronics and longer cables, 1-2% is better. For an inverter, you want as little loss as possible, ideally under 1%.

Should I use stranded or solid wire in a camper van?

Always use stranded (fine-strand) wire in a camper van. Solid wire can break from vibrations while driving. Look for automotive-grade wire such as FLRY or GXL that is rated for vehicle use.

What is the difference between mm² and AWG?

mm² is the cross-sectional area of the copper core; AWG is an American gauge number where a lower number means a thicker cable. They do not convert exactly. The common pairs: 1.5 mm² is 16 AWG, 2.5 mm² is 14 AWG, 4 mm² is 12 AWG, 6 mm² is 10 AWG, 10 mm² is 8 AWG, 16 mm² is 6 AWG and 25 mm² is 4 AWG. If you fall between two sizes, choose the thicker one.

Can a cable be too thick?

Technically no: a thicker cable is always safer and loses less voltage. Practically yes. Thick cable is expensive, heavy, hard to route through tight corners and needs larger lugs and a heavier crimping tool. Your fuse has to match the cable too. So choose the thinnest cable that both carries the current and stays within your voltage drop limit, and when in doubt go one size up.

Why do I need thinner cables at 24V?

At the same wattage, current halves when you double the voltage, and at the same time you are allowed twice the absolute voltage loss for the same percentage. Those two effects together mean that at 24V you need roughly a quarter of the copper cross-section you would use at 12V. That is the main reason to choose 24V for larger installations, from around 2 kW of inverter power upwards.

Do I need to account for cable temperature?

Yes. A cable's ampacity applies at around 30 °C. When it gets hotter the cable can carry less current: roughly 9% less at 40 °C, roughly 18% less at 50 °C and roughly 29% less at 60 °C. That matters mainly in the engine bay, right next to a heater, or where cables are bundled tightly and cannot cool each other. Our cable calculator and fuse calculator both apply this correction when you enter an ambient temperature.

How to calculate wire gauge for your camper van

One of the most important decisions in your camper van electrical installation is choosing the right wire gauge. Cables that are too thin lead to voltage drop, heat build-up and in the worst case fire. In this guide we explain step by step how to calculate the correct wire gauge.

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Why wire gauge matters so much

In a camper van you work with 12V (or 24V) DC power. At the same wattage, 12V draws much more current than 230V AC at home. More current means more heat generated in the cable. A cable that is too thin for the current flowing through it will get hot and can melt or cause fire. Additionally, a cable that is too thin causes voltage drop along the way. If your fridge needs 12V but only 11V arrives due to cable losses, it won't work properly or may even shut off.

How to calculate the right wire gauge

To calculate the wire gauge you need three pieces of information: 1. The current (in Amps) — how much current does the device draw? 2. The cable length (in meters) — the one-way distance from battery to consumer (the factor 2 in the formula accounts for the return cable) 3. The maximum voltage drop (%) — how much loss is acceptable? For 12V systems, a maximum of 3% voltage drop is generally recommended. For longer cables or sensitive equipment, 1-2% is better. The formula: cross-section (mm²) = (2 × length × current) / (56 × allowed voltage drop in volts) The number 56 is the conductivity of copper. For aluminum cables, use 34.

Common wiring mistakes to avoid

The most common mistake is forgetting that current has to travel both ways. A fridge 3 metres from the battery needs 6 metres of cable in total (positive + negative). Our formula already accounts for this with the factor 2, so you enter the one-way distance — but make sure you actually buy enough cable for both runs. Another common mistake is forgetting the fuse. Every cable must be protected with a fuse that matches the maximum current rating of that cable, not the connected device. Finally: never use household cables (Romex, NM-B) in a camper van. These are designed for 230V AC and don't have the right insulation for an environment with vibration and moisture.

Recommended wire gauges for common circuits

Here are guidelines for typical camper van circuits at 12V: • LED lighting (1-2A): 1.5 mm² up to 3m, 2.5 mm² up to 5m • USB chargers (2-3A): 1.5 mm² up to 2m, 2.5 mm² up to 4m • Fridge (5-8A): 2.5 mm² up to 3m, 4 mm² up to 5m • Water pump (5-10A): 2.5 mm² up to 2m, 4 mm² up to 4m • Inverter 1000W (85A+): 25 mm² up to 1.5m, 35 mm² up to 2.5m These are guidelines — always use a calculator for your specific situation.

Ampacity or voltage drop: which one decides?

There are two reasons to pick a thicker cable, and they have nothing to do with each other. The first is ampacity: how much current a cable can carry without getting too hot. That is a safety limit. These are the values we use for copper cable in a camper van: • 1.5 mm² (16 AWG): 10 A • 2.5 mm² (14 AWG): 16 A • 4 mm² (12 AWG): 21 A • 6 mm² (10 AWG): 28 A • 10 mm² (8 AWG): 40 A • 16 mm² (6 AWG): 60 A • 25 mm² (4 AWG): 80 A • 35 mm² (2 AWG): 100 A • 50 mm² (1/0 AWG): 125 A The second is voltage drop: how much voltage is lost along the way. That is a performance limit, not a safety limit. Which of the two decides depends on the length. On short runs with high current, ampacity governs. On long runs with modest current, voltage drop governs, and you often end up with a thicker cable than ampacity strictly requires. An example: 10 A over 1 metre fits on 1.5 mm² as far as ampacity goes, but over 8 metres you already need 4 mm² to stay within 3% voltage drop. Same current, completely different cable. Our cable calculator works out both limits and picks the thicker of the two.

Converting between mm² and AWG

In Europe cable is specified in mm², the cross-sectional area of the copper core. In American documentation and on many imported parts you will find AWG (American Wire Gauge) instead. That is a gauge number where a lower number means a thicker cable, which is confusing if you are not used to it. The common equivalents: • 0.75 mm² = 18 AWG • 1.5 mm² = 16 AWG • 2.5 mm² = 14 AWG • 4 mm² = 12 AWG • 6 mm² = 10 AWG • 10 mm² = 8 AWG • 16 mm² = 6 AWG • 25 mm² = 4 AWG • 35 mm² = 2 AWG • 50 mm² = 1/0 AWG • 70 mm² = 2/0 AWG Note that this is not an exact conversion. The AWG series does not line up with the European sizes, so the table gives the nearest common size each time. If you fall between two sizes, take the thicker one. And judge the core, not the outer diameter: cheap cable sometimes has a thick jacket around a thin core, which looks solid in a webshop photo but is not.

12V or 24V: what it does to cable thickness

At the same wattage, current halves when you go from 12V to 24V. A 2000 W inverter draws roughly 167 A at 12V and roughly 83 A at 24V. That helps twice over: there is less current, and you are also allowed twice the absolute voltage loss for the same percentage. Together that means at 24V you need roughly a quarter of the copper cross-section for the same distance and the same power. On a system with a large inverter that is a serious saving in money and hassle: 25 mm² can still be bent and crimped by hand, 95 mm² cannot. The trade-off is that the choice of 12V appliances is far wider, and that 12V consumers need a DC-DC converter. As a rule of thumb: below 2 kW of inverter power 12V is fine, above that 24V quickly becomes attractive.

Which type of cable belongs in a camper van?

Cross-section is not the only thing that matters. The type of cable determines whether your installation survives years in a vehicle that vibrates, heats up and sees moisture. Use fine-stranded (flexible) cable. Solid wire breaks from driving vibration, usually right at the terminal where you cannot see it. Automotive cable such as FLRY-B or GXL is made for this. Tinned copper is worth it anywhere moisture reaches: under the floor, near the water tank, around doors. The tin layer protects against corrosion that otherwise creeps along under the insulation. For conductivity it makes practically no difference; you can calculate with the same values as bare copper. Check the temperature rating of the insulation if the cable runs through the engine bay or past a heater. And use grommets wherever a cable passes through sheet metal, because a sharp edge will chafe through the insulation within a few thousand kilometres. What not to use: building wire from the hardware store. That is made for fixed 230V installations inside a wall, not for an environment full of vibration.

Calculate it yourself

Use our free tools to calculate the right wire gauge and fuse for your camper van installation.

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Frequently asked questions

What wire gauge do I need for 12V in a camper van?: This depends on the current and cable length. For light circuits (lighting, USB) 1.5-2.5 mm² is sufficient. For heavier consumers like a fridge or water pump, use 4-6 mm². For an inverter you need 25-50 mm². Always use a calculator for your specific situation.
How much voltage drop is acceptable in a camper van?: For most 12V circuits, a maximum of 3% is recommended (0.36V at 12V). For sensitive electronics and longer cables, 1-2% is better. For an inverter, you want as little loss as possible, ideally under 1%.
Should I use stranded or solid wire in a camper van?: Always use stranded (fine-strand) wire in a camper van. Solid wire can break from vibrations while driving. Look for automotive-grade wire such as FLRY or GXL that is rated for vehicle use.
What is the difference between mm² and AWG?: mm² is the cross-sectional area of the copper core; AWG is an American gauge number where a lower number means a thicker cable. They do not convert exactly. The common pairs: 1.5 mm² is 16 AWG, 2.5 mm² is 14 AWG, 4 mm² is 12 AWG, 6 mm² is 10 AWG, 10 mm² is 8 AWG, 16 mm² is 6 AWG and 25 mm² is 4 AWG. If you fall between two sizes, choose the thicker one.
Can a cable be too thick?: Technically no: a thicker cable is always safer and loses less voltage. Practically yes. Thick cable is expensive, heavy, hard to route through tight corners and needs larger lugs and a heavier crimping tool. Your fuse has to match the cable too. So choose the thinnest cable that both carries the current and stays within your voltage drop limit, and when in doubt go one size up.
Why do I need thinner cables at 24V?: At the same wattage, current halves when you double the voltage, and at the same time you are allowed twice the absolute voltage loss for the same percentage. Those two effects together mean that at 24V you need roughly a quarter of the copper cross-section you would use at 12V. That is the main reason to choose 24V for larger installations, from around 2 kW of inverter power upwards.
Do I need to account for cable temperature?: Yes. A cable's ampacity applies at around 30 °C. When it gets hotter the cable can carry less current: roughly 9% less at 40 °C, roughly 18% less at 50 °C and roughly 29% less at 60 °C. That matters mainly in the engine bay, right next to a heater, or where cables are bundled tightly and cannot cool each other. Our cable calculator and fuse calculator both apply this correction when you enter an ambient temperature.