Voltage Drop Calculator

Name: Voltage Drop Calculator
Author: True Calculator automated test suite

Find voltage drop and wire size for copper or aluminium cables — single phase, three phase and DC, with AWG sizes and conductors in parallel.

Wire size input

Wire size (AWG)

One-way cable length

Load current

Supply voltage

Length unit

Material

System

Conductors in parallel

Voltage drop

0.45 V

Drop as % of supply

0.205%

Typically should stay under 3%

Voltage at end of cable

219.55 V

220 V supply minus drop

DC / single-phase: drop = 2 × L × I × ρ / (A × n). Three-phase uses √3 instead of 2. Copper ρ = 0.0172, aluminium ρ = 0.0282 Ω·mm²/m, n = sets of conductors in parallel.

AWG wire sizes

AWG	Area (mm²)	Copper (Ω/km)	Aluminium (Ω/km)
4/0 AWG	107	0.161	0.264
3/0 AWG	85	0.202	0.332
2/0 AWG	67.4	0.255	0.418
1/0 AWG	53.5	0.321	0.527
1 AWG	42.4	0.406	0.665
2 AWG	33.6	0.512	0.839
3 AWG	26.7	0.644	1.056
4 AWG	21.2	0.811	1.33
6 AWG	13.3	1.293	2.12
8 AWG	8.37	2.055	3.369
10 AWG	5.26	3.27	5.361
12 AWG	3.31	5.196	8.52
14 AWG	2.08	8.269	13.558
16 AWG	1.31	13.13	21.527
18 AWG	0.823	20.899	34.265
20 AWG	0.518	33.205	54.44

Last updated: August 2026

How this calculator is verified

Checked by True Calculator automated test suite on 23 August 2026

Formula verified against a published worked example in the automated test suite
Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests

The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.

When to Use This Calculator

Use this calculator when planning wiring for a home extension, a shed, a borewell pump, or an inverter installation where the battery or mains sits far from the load. Long runs of cable on Indian construction sites and rural properties are where voltage drop shows up as dim bulbs, slow motors and overheating wires. Before buying cable, enter the run length, the load current of the appliances, and the available gauge sizes to see which one keeps the drop within limits. The same calculation helps electricians quote for jobs, owners compare copper against cheaper aluminium, and solar installers size the DC wiring between panels and inverter, where low-voltage circuits are especially sensitive to loss.

How to Use This Calculator

Step 1: Measure the one-way cable length from the supply to the load in metres.
Step 2: Enter the expected load current in amps and the conductor cross-section in mm².
Step 3: Choose copper or aluminium and single- or three-phase, then enter the supply voltage.
Step 4: Compare the drop percentage against the 3% guideline for lighting circuits.

Worked Example

A 230 V single-phase supply feeds a 10 A load through 20 m of 2.5 mm² copper wire. Enter length 20, current 10, area 2.5, copper, single phase and 230 V. The calculator computes 2 × 20 × 10 × 0.0172 ÷ 2.5 = 2.752 V, which is 1.2% of 230 V — comfortably inside the usual 3% limit. Switching to aluminium raises the drop to 4.512 V, or 1.96%, showing why copper is preferred for long runs.

Tips and Common Mistakes

•Tip 1: Keep drops under 3% for lights and 5% overall from the meter for general power circuits.
•Tip 2: Enter the one-way distance; the calculator adds the return path automatically.
•Tip 3: When in doubt between cable sizes, pick the next larger mm² — it halves the drop.
✗Mistake 1: Avoid entering the total of both conductors as the length — double counting inflates the drop.
✗Mistake 2: Don't ignore the supply voltage field; without it you get the drop in volts but no percentage to judge against.

Frequently Asked Questions

What is voltage drop?

Voltage drop is the loss of potential along a cable caused by its resistance. For a 20 m copper run of 2.5 mm² wire carrying 10 A, the drop works out to about 2.75 V, or 1.2% of a 230 V supply.

Why does the calculator use 2 × length for single phase?

The current travels out along one wire and back along the other, so the total conductor length is twice the one-way distance. Three-phase systems use √3 × length instead because the phases share the return path.

How much voltage drop is acceptable?

Most installations aim to keep drop under 3% for lighting circuits and under 5% overall from the meter to the farthest point. Above that, motors may run weak and lights can flicker noticeably.

Does copper really drop less than aluminium?

Yes — copper has a resistivity of 0.0172 Ω·mm²/m versus 0.0282 Ω·mm²/m for aluminium, so a copper cable of the same size drops roughly 40% less voltage for the same current and length.

How do I reduce voltage drop?

Use a larger cross-section cable, shorten the run, or raise the supply voltage. Doubling the cross-section halves the drop, which is why the calculator takes the wire area in mm² as an input.

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