Long cable runs lose voltage, so lights dim and motors struggle. Electrical codes typically recommend keeping the drop below 3–5%. Thicker wire, shorter runs or a higher supply voltage reduce the drop.
How to use the Voltage Drop Calculator
- Current type
- Conductor material
- Size given in
- Wire gauge (AWG, use −1 for 2/0, −2 for 3/0…)
- Cross-section area
- Parallel conductors per phase
- One-way cable length
- Load current
- Source voltage
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose the current type, conductor material and size, then enter the one-way length, current and source voltage.
Inputs explained
| Field | What to enter |
|---|---|
| Current type | Choose one: DC, AC single-phase, AC three-phase |
| Conductor material | Choose one: Copper, Aluminium |
| Size given in | Choose one: AWG, mm² |
| Wire gauge (AWG, use −1 for 2/0, −2 for 3/0…) | A number |
| Cross-section area | Units: mm², cm², m², in² |
| Parallel conductors per phase | A number |
| One-way cable length | Units: m, cm, mm, km, in, ft … |
| Load current | Units: A, mA, µA, kA |
| Source voltage | Units: V, kV, mV |
What each result means
- Effective conductor area = [A]
- Voltage drop percentage = [Voltage drop]÷[Source voltage]×100
- Voltage at the load = [Source voltage] – [Voltage drop]
Example values
How the main result changes when Wire gauge changes and everything else stays at the example values above:
| Wire gauge (AWG, use −1 for 2/0, −2 for 3/0…) | Voltage drop (V) |
|---|---|
| 6 | 6.6048 |
| 9 | 6.6048 |
| 12 | 6.6048 |
| 15 | 6.6048 |
| 18 | 6.6048 |
| 24 | 6.6048 |
Formula
DC / 1-phase: V_d = 2·I·R·L · 3-phase: V_d = √3·I·R·L, R = ρ/A (per conductor, per metre)
Worked example
Inputs — Current type: AC single-phase; Conductor material: Copper; Size given in: mm²; Cross-section area: 2.5 mm²; Parallel conductors per phase: 1; One-way cable length: 30 m; Load current: 16 A; Source voltage: 230 V.
Results — Effective conductor area = 2.5 mm²; Voltage drop = 6.6048 V; Voltage drop percentage = 2.8717 %; Voltage at the load = 223.3952 V; Assessment = OK (below 3%).
Key terms
- AWG
- American Wire Gauge, smaller numbers are thicker.
Frequently asked questions
What voltage drop is acceptable?
Typically up to 3% for branch circuits and 5% overall.
Why is the length doubled for single-phase?
Current flows out and back through two conductors.
How do I reduce voltage drop?
Use a larger cable, a shorter run or a higher voltage.
Does temperature matter?
Yes – resistance rises with conductor temperature.