Estimate the required DC cable cross-section from system voltage, current, distance, material, and allowable voltage drop.
This calculator uses a simple two-conductor DC voltage-drop method. Final cable selection should also consider insulation temperature, grouping, routing method, and current-carrying capacity.
Low-voltage DC systems are much more sensitive to cable losses than many AC circuits. A small voltage drop that looks harmless on a 230 V circuit can become a large percentage loss on a 12 V, 24 V, or 48 V battery system. That is why cable sizing is one of the most important design checks in solar charge circuits, battery banks, DC distribution panels, telecom systems, and inverter supply wiring.
This DC cable size calculator estimates the minimum conductor cross-section needed to keep voltage drop within the chosen limit. It uses current, one-way cable length, conductor resistivity, and system voltage to calculate the required cross-sectional area in square millimetres, then suggests the next common cable size and reports the resulting actual voltage drop.
It is especially useful when you need to choose between 6 mm2, 10 mm2, 16 mm2, or larger cables quickly without manually rearranging the voltage-drop formula each time.
| Input | Meaning | Unit |
|---|---|---|
| System Voltage | Nominal DC bus or load voltage | V |
| Current | Expected continuous circuit current | A |
| One-Way Length | Distance from source to load | m |
| Allowable Voltage Drop | Maximum acceptable drop as a percentage of system voltage | % |
| Material | Resistivity basis for copper or aluminum conductor | ohm mm2/m |
The voltage is entered in volts, current in amperes, and cable length in metres. The recommended conductor size is shown in square millimetres because that is the most common metric size system used for solar, battery, and industrial DC cabling. The output also reports the actual voltage drop in volts and percent once a nearby standard cable size has been selected.
System voltage = 24 V, current = 45 A, one-way length = 18 m, drop limit = 3%, copper conductor
Allowable drop = 24 x 0.03 = 0.72 V
Required area = 2 x 0.0175 x 18 x 45 / 0.72 = 39.38 mm2
The next common size is 50 mm2, and the actual drop on 50 mm2 becomes about 0.57 V, or 2.36%.
System voltage = 48 V, current = 22 A, one-way length = 25 m, drop limit = 2%, copper conductor
Allowable drop = 0.96 V
Required area = 2 x 0.0175 x 25 x 22 / 0.96 = 20.05 mm2
A 25 mm2 cable is the next standard choice and keeps the drop just below the selected limit.
The result from this calculator is based on voltage drop only. That makes it very useful for first-pass sizing, but it does not replace ampacity checks. A cable may satisfy voltage drop and still be unsuitable if installation temperature, grouping, insulation type, conduit fill, or termination temperature limits reduce its current-carrying capacity. In the same way, a cable selected for ampacity alone may still create too much drop on a long DC run.
In practice, good DC design checks both conditions. Use this page to find a sensible cross-section for loss control, then confirm the selected cable against the applicable wiring rules, installation method, and product data. That combination gives a much more dependable answer for battery systems, charge controllers, DC loads, and inverter supply cables.