Wire Voltage Drop Calculator
Calculate the voltage lost in a cable and the heat it produces from the wire size (AWG or mm²), length and current.
Formula and cautions
R = ρ·L / A and ΔV = I·R. Current flows out on one wire and back on the other, so the round-trip length is normally used. At low DC voltages such as 12 V or 5 V a small drop is a large share of the supply, which is why LED strips and motors often misbehave on long runs. This tool covers voltage drop only. How much current a wire can safely carry depends on its insulation and installation, so check the cable's ampacity rating separately.
Frequently asked questions
How much voltage drop is acceptable?
A common guideline is 3% or less for a single run and 5% or less overall. Low-voltage DC loads such as LED strips and small motors benefit from staying near 3% or below.
How do AWG and mm² sizes compare?
AWG is the American wire gauge, where a smaller number means a thicker wire. Metric sizes give the copper cross-section in mm² directly. AWG 18 is about 0.82 mm², close to 0.75 mm² metric wire.