About this calculator

Voltage drop = 2 × L × I × ρ / A for single-phase circuits. ρ (copper) ≈ 0.0175 Ω·mm²/m, (aluminium) ≈ 0.028. Aim to keep total drop under 3% for lighting, 5% for power.

How it works

Enter your one-way cable length (m), current (a), conductor area (mm²), conductor and system voltage (v). The result updates as you type, using the formula shown below. Nothing you enter is stored.

Limits

Results are theoretical and ignore installation method and grouping. Mains work must meet local wiring rules (BS 7671 in the UK).

Who it's for

Electricians, students and DIYers checking loads, cables and running costs.

Formula: Vd = 2 × L × I × ρ / A

Frequently asked questions

What does the Voltage Drop Calculator do?

Estimate voltage drop along a copper or aluminium cable run for any load. Voltage drop = 2 × L × I × ρ / A for single-phase circuits. ρ (copper) ≈ 0.0175 Ω·mm²/m, (aluminium) ≈ 0.028. Aim to keep total drop under 3% for lighting, 5% for power.

Is the Voltage Drop Calculator free to use?

Yes. Every calculator on Calcurly.com is free, works in your browser without sign-up, and can be embedded on your own website.

How accurate is the Voltage Drop Calculator?

Results are calculated in real time using the formula Vd = 2 × L × I × ρ / A. Treat the output as a well-informed estimate — always cross-check with local regulations, product datasheets, or a qualified electrical professional before committing to a purchase or a job.

What inputs does the Voltage Drop Calculator need?

Enter values for: One-way cable length (m), Current (A), Conductor area (mm²), Conductor, System voltage (V). Sensible defaults are pre-filled where possible so you can start with a single change.

Can I embed the Voltage Drop Calculator on my own website?

Yes — copy the iframe snippet at the bottom of this page, or use the Embed Generator to customise the size. The embedded version stays in sync with the live calculator on Calcurly.com.