Cable Length & Voltage Drop Calculator
Calculate voltage drop, power loss and remaining voltage for your DC/AC cable runs. Enter your circuit parameters below to get instant results and wire size recommendations.
Voltage Drop Calculator
Calculation Results
How This Calculator Works
This voltage drop calculator uses the standard resistivity formula: Vdrop = I × R × L × 2 (factor of 2 accounts for the return path in DC circuits). Wire resistance is adjusted for temperature using the coefficient of the selected material. Copper has a resistivity of 0.01724 Ω·mm²/m and aluminum 0.02826 Ω·mm²/m at 20°C. A voltage drop below 3% is generally acceptable for most DC applications; below 5% for AC power circuits.
Frequently Asked Questions
What is an acceptable voltage drop?
For DC circuits, a voltage drop of less than 3% is generally recommended. For AC power circuits, up to 5% is typically acceptable. Sensitive electronics may require even tighter tolerances (<2%).
Copper or aluminum — which is better?
Copper has about 60% lower resistivity than aluminum, meaning less voltage drop for the same wire size. However, aluminum is lighter and cheaper. For the same performance, aluminum wire needs to be about 1.6× larger in cross-section.
How does temperature affect voltage drop?
As temperature increases, wire resistance increases (positive temperature coefficient). At 80°C, copper resistance is about 25% higher than at 20°C, resulting in proportionally higher voltage drop. Always use the expected operating temperature for accurate results.
Should I use the total cable run or one-way length?
Enter the one-way cable length. This calculator automatically multiplies by 2 to account for the return path (out and back), which is standard practice for DC voltage drop calculations.
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