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DC Voltage Drop Calculator

Estimate voltage drop in a two-conductor DC circuit, or find the minimum cross-section for a chosen drop target. Enter the one-way length; the model doubles it.

What do you want to work out?
V
A
m
mm²
Advanced settings
Ω·mm²/m
 

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How the DC voltage drop calculation works

The calculator estimates voltage drop in a two-conductor DC circuit. Enter the one-way cable length; the model doubles it because current travels to the load and back. Resistance is calculated from conductor resistivity, loop length and cross-sectional area. The tool then calculates voltage drop, percentage drop, estimated load voltage and cable loss. In minimum area mode it rearranges the same equation for a selected voltage-drop target. The result is an electrical estimate at the displayed resistivity, not a complete cable safety design.

Loop length (m) = 2 × one-way length

Resistance (Ω) = resistivity (Ω·mm²/m) × loop length ÷ area (mm²)

Voltage drop (V) = current (A) × resistance (Ω)

Voltage drop (%) = voltage drop ÷ system voltage × 100

Cable loss (W) = current² × resistance

Minimum mathematical area (mm²) = resistivity × loop length × current ÷ allowed drop V

Worked examples

12 V, 10 A, 5 m one way, copper model 0.0175 and 2.5 mm²: loop 10 m, 0.0700 Ω, 0.70 V drop (5.83%), 11.30 V at the load and 7.00 W loss.

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24 V, 20 A, 10 m one way, copper model 0.0175 and 6 mm²: 0.05833 Ω, 1.1667 V drop (4.86%), 22.8333 V at the load and 23.3333 W loss.

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12 V, 10 A, 5 m one way, copper model and a 3% target: maximum drop 0.36 V and minimum mathematical area 4.8611 mm². This is not automatically a safe cable size.

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Frequently asked questions

Why is the cable length doubled?

The entered length is one way. A two-conductor DC circuit has an outgoing and return conductor, so both contribute resistance.

What is conductor resistivity?

It is the material parameter used to relate length and cross-section to resistance. The displayed defaults are editable model values at 20°C.

Why does aluminium show more drop than copper?

With the displayed model values, aluminium has higher resistivity, so the same length, area and current produce more resistance.

Why can measured voltage drop differ?

Real resistance depends on conductor temperature, material, terminals, joints, actual length and manufacturing tolerances.

What voltage-drop percentage should I choose?

Use the limit required by the load, system design and applicable manufacturer or installation requirements. This calculator does not impose one universal target.

Is the calculated minimum area a safe wire size?

No. It addresses voltage drop only. Ampacity, insulation, temperature, installation method, fault current and protection must be checked separately.

Can I use this calculator for AC wiring?

The MVP models a two-conductor DC circuit. It does not account for AC reactance, phase, power factor or multi-phase systems.

What if calculated drop equals or exceeds supply voltage?

The assumed circuit is not useful in this simple model. Increase voltage or conductor area, reduce length or current, and verify the complete design rather than relying on a negative load voltage.

Sources