Cable Size Calculator for 12V, 24V and 60V Systems
Use this free cable size calculator to estimate the correct cable cross-section for automotive, campervan, marine and off-grid DC circuits. Enter voltage, load, one-way cable length and allowed voltage drop to get a recommended cable size, estimated voltage drop and suggested fuse size.
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Cable overview
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How to use the cable size calculator
Select system voltage, then choose whether to enter the load as current in amps or power in watts. Enter one-way cable length and your acceptable voltage drop. The calculator uses the full circuit length automatically and estimates the minimum cable cross-section needed to stay within your chosen target.
This calculator supports 12V, 24V and 60V DC systems commonly used in vehicles, leisure batteries, solar setups and off-grid installations.
- Use amps if you already know current draw.
- Use watts if you only know appliance power. The calculator will estimate current automatically.
- Use one-way cable length only. The return path is added automatically.
- Choose Auto for voltage drop if you want a sensible default for the selected circuit type.
Why cable size matters
Choosing the correct cable size is one of the most important steps in any 12V, 24V or 60V installation. If the cable is too small, voltage drop increases, equipment may perform poorly and the cable may overheat. Selecting an appropriate cable size helps reduce energy loss, improves reliability and supports safe operation. Correct cable sizing also helps prevent overheating and protect connected equipment.
Typical voltage drop targets for 12V and 24V systems
| Circuit type | Typical voltage drop target | Notes |
|---|---|---|
| Lights, electronics, sensitive loads | 3% | Best where stable voltage is important. |
| Pumps, fans, sockets, general accessories | 5% | Common target for everyday low-voltage accessory circuits. |
| Less critical circuits | Up to 10% | May be acceptable in some non-sensitive applications. |
| Solar and charging circuits | 3% | Lower drop is usually preferred for charging efficiency. |
Typical automotive copper cable sizes explained
| Cable size | Typical use |
|---|---|
| 1.0 mm² | Very light loads, low-current signal or lighting circuits |
| 1.5 mm² | Small accessories, light-duty circuits |
| 2.5 mm² | Fridges, pumps, medium-load 12V circuits |
| 4.0 mm² | Heavier accessory circuits and longer runs |
| 6.0 mm² | Battery charging, DC-DC chargers, medium-high current use |
| 10.0 mm² and above | Battery cables, inverter supply and high-current systems |
Supported cable types
This calculator is designed for copper cable typically used in:
- Battery connections
- DC accessory circuits
- Solar charge controller wiring
- Inverter supply cables
- Campervan electrical systems
- Marine low-voltage installations
Example calculations
Example 1: A 12V fridge drawing 5A over a 4m one-way run will usually need a larger cable than a short lighting circuit because low-voltage systems are sensitive to voltage drop.
Example 2: A 12V water pump drawing 10A over a 5m one-way cable run may require a medium cable size to stay within a 3% or 5% drop limit.
Example 3: A 24V circuit drawing 15A over 6m one-way can often use a smaller cable than an equivalent 12V circuit because the higher voltage reduces the relative voltage drop.
Example 4: A 60V circuit carrying 10A over a 5m run typically requires a smaller cable than an equivalent 12V system because higher voltage reduces relative voltage drop.
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FAQ
The correct cable size depends on current, cable length and acceptable voltage drop. Low-voltage 12V systems are especially sensitive to cable losses, so longer runs often need significantly larger cable.
Yes. If you only know appliance power, enter watts and the calculator will estimate current using power divided by system voltage.
The longer the cable, the higher the resistance of the circuit. That increases voltage drop and may require a larger cable size to keep the system working properly.
In many practical installations, yes. Going up one cable size can help reduce voltage drop further and provide extra margin for performance and reliability.
This tool suggests a fuse based on around 125% of the calculated load current, rounded up to a common fuse size. Always verify the fuse against cable rating, connector rating and equipment requirements.
Battery cable size depends on inverter power, cable length and system voltage. Use this calculator to estimate minimum cable cross-section and then verify against fuse rating and manufacturer guidance.
These calculator results are provided as a practical technical guide only. Final cable sizing should always be verified against installation method, ambient temperature, insulation type, bundling conditions, connector ratings and applicable electrical standards. Always confirm cable selection with manufacturer data before installation.