# Voltage Drop Calculator

URL: https://speedycalculator.com/calculators/physics/voltage-drop/
Last updated: 2026-10-30

> The voltage drop calculator finds the voltage lost in a cable run for DC, single-phase or three-phase circuits from the conductor material, size (AWG or mm²), length and current, plus the percentage drop and voltage at the load.

## Inputs

- Current type
- Conductor material
- Size given in
- Wire gauge (AWG, use −1 for 2/0, −2 for 3/0…)
- Cross-section area (mm², cm², m², in²)
- Parallel conductors per phase
- One-way cable length (m, cm, mm, km, in, ft, yd, mi)
- Load current (A, mA, µA, kA)
- Source voltage (V, kV, mV)

## Results

- Effective conductor area
- Voltage drop
- Voltage drop percentage
- Voltage at the load
- Assessment

## 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)
```

## Explanation

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

FieldWhat to enterCurrent typeChoose one: DC, AC single-phase, AC three-phaseConductor materialChoose one: Copper, AluminiumSize given inChoose one: AWG, mm²Wire gauge (AWG, use −1 for 2/0, −2 for 3/0…)A numberCross-section areaUnits: mm², cm², m², in²Parallel conductors per phaseA numberOne-way cable lengthUnits: m, cm, mm, km, in, ft …Load currentUnits: A, mA, µA, kASource voltageUnits: 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)66.604896.6048126.6048156.6048186.6048246.6048

## 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.

## FAQ

**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.


## Sources

- [The Engineering ToolBox](https://www.engineeringtoolbox.com/)
- [NFPA 70 – National Electrical Code (informational notes on voltage drop)](https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70)