Electrical
Voltage Drop Calculator
Compare conductor voltage loss across single-phase and three-phase runs using the actual route length and expected load.
Result
Electrical work is life-safety work governed by the NEC or your local code, and must be designed and installed by a licensed electrician. Conductor and overcurrent sizing depends on ambient temperature, conductor bundling, termination ratings, continuous-load rules and more. This is an educational estimate and must never be used as the basis for an installation. The 3% branch-circuit and 5% total guideline is an NEC recommendation in informational notes, not a hard requirement, but exceeding it causes dim lights, poor motor starting and wasted energy.
Get a Free Business AuditWhat moves the number
- One-way distance includes the installed route, not just the floor-plan separation.
- Conductor area and material affect resistance.
- The selected phase model changes the drop calculation.
Where this one goes wrong
A steady running-current estimate may miss a short starting dip. This tool also does not model every upstream loss, connection condition or AC impedance effect. A passing percentage alone does not prove satisfactory equipment operation.
Questions
About this calculator
Should I double the cable distance?
Enter the one-way run requested by the form. The calculation applies its own circuit factor, so doubling the entry would count the return path again.
Does the percentage include the feeder?
Only the run entered here is represented. Assess the complete supply path separately when a branch begins at a distant distribution board.
Is the displayed guideline a compliance verdict?
No. Voltage-drop design is a planning check against local code, project specifications and equipment requirements; ampacity and protection require their own verification.
The formula
single phase: VD = 2 × K × I × L ÷ circular mils (K = 12.9 copper, 21.2 aluminium)
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How to use this calculator
- Conductor size (AWG). Enter your own figure; the page starts at 10 AWG.
- Conductor material. Enter your own figure; the page starts at Copper.
- Load current (A). Enter your own figure; the page starts at 20.
- One-way run length (ft). Enter your own figure; the page starts at 120.
- System voltage (V). Enter your own figure; the page starts at 240.
- Phase. Enter your own figure; the page starts at Single phase.
The result updates as you type, so you can try a figure, see what it does to voltage drop, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Conductor size (AWG) | 10 AWG |
| Conductor material | Copper |
| Load current (A) | 20 |
| One-way run length (ft) | 120 |
| System voltage (V) | 240 |
| Phase | Single phase |
What comes out
| Result | Value |
|---|---|
| Voltage drop main result | 6.0 |
| Drop as a percentage | 2.49% |
| Voltage at the load | 234.0 |
| Against the 3% guideline | Within the 3% guideline |
Drop is 6.0 V (2.49%), leaving 234.0 V at the load, within the 3% guideline.
How sensitive the answer is
Holding everything else steady and changing only load current (a), this is what happens to voltage drop. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Load current (A) | Voltage drop |
|---|---|
| 10 | 3.0 |
| 15 | 4.5 |
| 20 example above | 6.0 |
| 30 | 8.9 |
| 40 | 11.9 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Conductor size (AWG)
- Choose from 14 AWG, 12 AWG, 10 AWG, 8 AWG, 6 AWG, 4 AWG, 3 AWG, 2 AWG, 1 AWG, 1/0 AWG, 2/0 AWG, 3/0 AWG, 4/0 AWG.
- Conductor material
- Choose from Copper, Aluminium.
- Load current (A)
- A number, between 0 and 5000, starting at 20.
- One-way run length (ft)
- A number, between 0 and 20000, starting at 120.
- System voltage (V)
- A number, between 0 and 100000, starting at 240.
- Phase
- Choose from Single phase, Three phase.
What the results tell you
| Result | What it is |
|---|---|
| Voltage drop | The headline result. A decimal figure. |
| Drop as a percentage | A percentage. |
| Voltage at the load | A decimal figure. |
| Against the 3% guideline | A category or planning selection, rather than a measured quantity. |
Before you rely on this number
Conductor sizing, voltage drop and load figures are governed by code, and the code takes precedence over any calculator. Ambient temperature, conduit fill, continuous load factors and the specific installation all change the answer. Treat this as a first pass, not a design.
Keep going
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