Electrical
Voltage Drop Calculator
Compare resistive voltage drop, conductor area and maximum cable length in one tool. AC estimates assume a balanced resistive load at unity power factor; results are not ampacity or code checks.
Change any input to update the calculation. Unit changes preserve the physical quantity.
Inputs
For three-phase, enter line-to-line voltage.
VConductor temperature, not ambient air; converted limits are −40 to 150 °C.
Planning criterion only; this value is not a code-compliance threshold.
%Calculated locally in your browser. No sign-up or input upload.
Results
Approximate voltage drop
2.759 VVoltage drop
11.494 %Approximate load voltage
21.241 VOne-way conductor resistance
0.13793 ΩApproximate conductor power loss
27.586 WConductor cross-sectional area
2.5 mm²One-way cable length
20 m65.617 ftCalculation breakdown
- Entered conductor
- 2.5 mm²
- Model
- Two-conductor DC resistive loop
Assumptions & checks
Wire sizing here is based on the voltage-drop criterion only. It does NOT establish ampacity, installation method, temperature derating or local electrical-code compliance.
Drop exceeds 3%. Compare with your chosen target and installation requirements; 3% is not a compliance verdict.
Calculated voltage drop exceeds your entered target.
Formula
Bulk resistance model with conductor temperature correction. AC uses unity power factor and neglects reactance, skin effect and connections.
Worked example
Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.
Inputs
- Circuit type
- DC · two-conductor
- Supply voltage
- 24 V
- Load current
- 10 A
- One-way cable length
- 20 m
- Conductor material
- Copper
- Conductor size notation
- mm²
- Conductor cross-sectional area
- 2.5 mm²
- Conductor operating temperature
- 20 °C
- Target voltage-drop limit
- 3 %
Result
- Approximate voltage drop
- 2.759 V
- Voltage drop
- 11.494 %
- Approximate load voltage
- 21.241 V
- One-way conductor resistance
- 0.13793 Ω
- Approximate conductor power loss
- 27.586 W
- Conductor cross-sectional area
- 2.5 mm²
- One-way cable length
- 20 m
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Frequently asked questions
Can the minimum size be used as a compliant wire selection?
No. It satisfies only the entered voltage-drop criterion in this simplified model. Ampacity, protection, installation, derating, terminations and local electrical rules still need a separate qualified check.
Should length include the return conductor?
Enter one-way route length. The DC and single-phase multiplier accounts for outgoing and return conductors. Balanced three-phase uses the square-root-of-three voltage-drop factor.
Why can AC results differ from a cable manufacturer's calculator?
This tool assumes unity power factor and bulk resistive conductors. Real cables have product-specific AC resistance and reactance; motors, connections, skin effect and unbalanced loads can change the result.
Reference data & method sources
- Schneider Electric: voltage-drop formulae
This calculator uses the resistive, unity-power-factor special case, not the guide's complete impedance model.
- NIST / Bureau of Standards: copper wire tables
Copper reference resistance and temperature coefficient. Bulk material estimates may differ from cable data.
- NIST / Bureau of Standards: aluminum wire tables
EC aluminum reference: 61% IACS resistivity and temperature coefficient at 20 °C.
Reference tables
Bulk conductor properties
Reference bulk properties, not a cable ampacity table. Stranding, alloys and AC effects can change product resistance.
| Material | ρ at 20 °C (Ω·mm²/m) | α at 20 °C (1/°C) |
|---|---|---|
| Annealed copper | 0.017241 | 0.00393 |
| EC aluminum (61% IACS) | 0.028264 | 0.00403 |
Listed metric conductor areas
Candidate size series for rounding the voltage-drop result upward. Availability and installation suitability must be checked separately.
| Area (mm²) |
|---|
| 0.5 |
| 0.75 |
| 1 |
| 1.5 |
| 2.5 |
| 4 |
| 6 |
| 10 |
| 16 |
| 25 |
| 35 |
| 50 |
| 70 |
| 95 |
| 120 |
| 150 |
| 185 |
| 240 |
| 300 |
| 400 |
| 500 |
| 630 |
AWG geometric cross-sectional areas
d = 0.127 × 92^((36−gauge)/39) mm; A = πd²/4. Sizes outside 4/0–40 AWG are not selected by this table.
| AWG | Area (mm²) |
|---|---|
| 4/0 | 107.2193 |
| 3/0 | 85.02877 |
| 2/0 | 67.43088 |
| 1/0 | 53.47512 |
| 1 | 42.4077 |
| 2 | 33.63083 |
| 3 | 26.67046 |
| 4 | 21.15064 |
| 5 | 16.77322 |
| 6 | 13.30177 |
| 7 | 10.54878 |
| 8 | 8.36556 |
| 9 | 6.63419 |
| 10 | 5.26115 |
| 11 | 4.17229 |
| 12 | 3.30877 |
| 13 | 2.62398 |
| 14 | 2.08091 |
| 15 | 1.65023 |
| 16 | 1.3087 |
| 17 | 1.03784 |
| 18 | 0.82305 |
| 19 | 0.65271 |
| 20 | 0.51762 |
| 21 | 0.41049 |
| 22 | 0.32553 |
| 23 | 0.25816 |
| 24 | 0.20473 |
| 25 | 0.16236 |
| 26 | 0.12876 |
| 27 | 0.10211 |
| 28 | 0.08098 |
| 29 | 0.06422 |
| 30 | 0.05093 |
| 31 | 0.04039 |
| 32 | 0.03203 |
| 33 | 0.0254 |
| 34 | 0.02014 |
| 35 | 0.01597 |
| 36 | 0.01267 |
| 37 | 0.01005 |
| 38 | 0.00797 |
| 39 | 0.00632 |
| 40 | 0.00501 |