Electrical & Electronics

DC Voltage Drop Calculator

Calculate cable voltage drop, load voltage and power loss with copper or aluminium, AWG or mm².

Your inputs

Your results

Voltage drop: —

Voltage at load: —

Voltage drop · %: —

Cable power loss: —

Loop resistance: —

Conductor area: —

—

Area for drop target: —

Maximum one-way length: —

FormulaR = ρ × 2L / A

Uses ideal conductors at 20 °C. Heating, contact losses and ampacity are not included. Area and length results apply only to your voltage-drop target.

Estimate DC cable voltage drop and compare conductor sizes

Estimate the voltage lost in a two-conductor DC cable, the voltage reaching the load and the power dissipated in the cable. Compare conductor sizes against your chosen voltage-drop target. The model assumes equal outgoing and return conductors with fixed resistivity at 20 °C; it excludes connections, temperature rise and the load's response to reduced voltage.

Step by step

Enter supply voltage and expected load current. Enter the one-way distance from the supply to the load, then choose metres or feet; the calculator includes the return path automatically.
Choose copper or aluminium and enter conductor cross-sectional area in mm², or select an AWG size. Set the maximum voltage-drop percentage you want to compare against.
Review voltage drop, load voltage, cable loss and target status. Compare the calculated minimum area and maximum one-way length, then change the conductor size to see the effect.

Settings and limits

Cable length and resistance: The model uses R = ρ × 2L / A, where L is one-way length and A is the area of each conductor. Entering the combined outgoing and return distance would count the loop twice. Both conductors are assumed to have the same material and area.
Area and AWG: The area is conductor cross-section, not cable diameter or the outer size including insulation. A smaller AWG number represents a larger conductor. The minimum-area result addresses your voltage-drop target only; it does not establish current-carrying capacity, protection requirements or installation compliance.
Target and operating assumptions: The target must be greater than 0% and below 100%. Copper and aluminium use different fixed resistivities, so the same size produces different losses. Current remains the value you entered; the tool does not simulate a constant-power load drawing more current as voltage falls.

Worked example

Enter 12 V, 5 A and a 10 m one-way copper cable. Select mm², enter 2.5 mm² and set a 3% target. Compare that result with the same cable at 6 mm² in the table below.

Expected result
A	ΔV	ΔV / Vs	Vload	Ploss
2.5 mm²	0.68964 V	5.747%	11.3104 V	3.4482 W
6 mm²	0.28735 V	2.39458%	11.7127 V	1.43675 W

At 2.5 mm², drop is 0.68964 V, or 5.747%, which exceeds the target. The calculated minimum area is about 4.78917 mm²; at 6 mm², drop falls to 0.28735 V, or 2.39458%. The original cable's maximum one-way length at the target is about 5.22011 m.

Questions and troubleshooting

Why is the load voltage shown as a dash?

A calculated drop equal to or greater than the supply leaves no positive load voltage in this fixed-current model. Check current, one-way length and conductor size. The result indicates incompatible assumptions rather than a prediction that a real load will keep drawing the entered current.

Does a passing target mean the cable is suitable?

It means only that the modeled drop is within your chosen percentage. Cable heating, routing, ambient conditions, connectors and protective devices are outside this calculation. Check those requirements separately before choosing an actual cable.

What happens with zero current?

Zero current produces zero voltage drop and zero cable loss. Maximum length is shown as unbounded because there is no drop to compare with the target. This mathematical result does not determine a practical installation length.