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Voltage Drop Calculator: DC, Single & Three Phase
Check voltage drop using copper or datasheet R/X. Results include the values and assumptions used.
Formula and worked example
ΔV = k × I × (L / 1000) × (R × PF + X × √(1 − PF²))
k = 2 for two-wire DC / single phase; √3 for balanced three phase.
Drop (%) = 100 × ΔV / supply voltage.
k = 2 for two-wire DC / single phase; √3 for balanced three phase.
Drop (%) = 100 × ΔV / supply voltage.
How to use the calculation
L is the one-way route length in metres; R and X describe one conductor in Ω/km. Copper estimate mode uses R20 = 1000 ÷ (58 × area) and R(T) = R20 × [1 + 0.00393 × (T − 20)]. That mode assumes unity PF and zero reactance. Datasheet mode uses your operating-temperature values. DC always uses PF = 1 and X = 0.
Worked example
For a 230 V DC circuit, 10 A, 100 m one-way length, 10 mm² standard annealed copper at 20°C, the model gives approximately 3.4483 V drop (1.4993%). The approximate receiving voltage is 226.5517 V.
Common questions
Do I enter the round-trip cable length?
Enter one-way length. The two-wire DC/single-phase formula already includes outgoing and return conductors.
Can this tell me the final cable size?
No. It calculates voltage drop for entered conductor data. Current capacity, derating, short-circuit withstand and protection coordination are separate cable-selection checks.
How can I use an aluminium cable or a motor load?
Select manufacturer/datasheet mode. Use the relevant cable R and X at operating conditions and the actual lagging load PF. For three phase, enter supply line-to-line voltage.
What if calculated drop reaches the supply voltage?
The tool marks receiving voltage as outside the model range. The entered operating point needs a different circuit design or a more complete circuit analysis.
Related electrical guides
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Formula references
Formula review: 31 October 2026. Examples are illustrative; use your actual equipment and project data.
