Free Online Calculators
Calculate cable cross-section & voltage drop
Choosing the right cable cross-section is one of the most critical decisions in any electrical installation. Whether you are wiring a new home, installing a solar power system, or upgrading your workshop, an undersized cable can lead to dangerous overheating, excessive voltage drop, and even fire. Our free cable cross-section calculator helps you determine the correct wire gauge in seconds – no engineering degree required.
Every electrical conductor has resistance. The thinner the cable, the higher the resistance – and the more energy is lost as heat. This energy loss is expressed as voltage drop, which reduces the performance of connected devices and can create a serious fire hazard. International standards such as IEC 60364 and national regulations require that voltage drop in a circuit does not exceed certain limits (typically 3–5%).
Conversely, using an excessively thick cable is wasteful and expensive. The goal is to find the smallest cross-section that safely carries the required current with acceptable voltage drop – and that is exactly what this calculator does.
The tool uses the fundamental formula of electrical engineering: A = (2 × L × I) / (σ × ΔU), where A is the cross-section in mm², L is the cable length in meters, I is the current in amperes, σ (sigma) is the electrical conductivity of the material, and ΔU is the permissible voltage drop in volts. The result is then rounded up to the next standard commercial cable size.
The calculator outputs the minimum required cross-section in mm², the actual voltage drop at that cross-section, and a recommendation for the next standard cable size available in the market (e.g., 1.5 mm², 2.5 mm², 4 mm², 6 mm², 10 mm², 16 mm²).
A ring main circuit in a living room carries a maximum of 16 A over a 25-metre cable run at 230 V AC. Using copper conductors and a 3% voltage drop limit, the calculator recommends a minimum cross-section of 1.5 mm² – the standard size for residential socket circuits in Europe.
A home EV charger rated at 7.4 kW (single phase, 230 V, ~32 A) installed 30 metres from the consumer unit requires a cross-section calculation. With a 3% voltage drop limit and copper cable, the result is approximately 6 mm² – much larger than many homeowners might assume.
Low-voltage DC systems are extremely sensitive to voltage drop. A 12 V refrigerator drawing 10 A over a 4-metre run needs at least a 4 mm² copper cable to stay within 3% drop. At 12 V, even a small resistance causes a disproportionately large voltage loss.
Even experienced installers sometimes make calculation errors. Watch out for these common pitfalls:
For a 20 A circuit at 230 V with a cable run of up to 20 metres, a 2.5 mm² copper cable is typically sufficient. For longer runs or higher loads, recalculate with the actual parameters.
According to IEC 60364, the recommended maximum voltage drop is 3% for lighting circuits and 5% for other loads. Some countries or applications may have stricter requirements.
Copper is the standard choice for residential wiring due to its superior conductivity, flexibility, and corrosion resistance. Aluminium is used in large-diameter supply cables because it is lighter and less expensive, but requires special connectors and care.
Absolutely. Enter the DC system voltage (e.g., 48 V), the maximum current from the panels, and the cable length. The calculator will give you the correct cross-section for your PV installation.
The calculator primarily focuses on voltage drop. Always verify that the selected cable also meets the ampacity requirements for your installation method and ambient temperature, as per relevant standards.