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Science & Engineering

Voltage Drop Estimator

Estimate voltage drop in copper or aluminium cable from length, size (mm² or AWG), current and circuit type.

Your inputs

Results

Voltage drop

6.621 V

Drop as % of supply
2.878%
Voltage at the load
223.38 V
Conductor cross-section
2.5 mm²
Power lost in the cable
105.9 W

≈Estimate based on the stated model and assumptions

Notes for this result

  • Uses DC resistance at 20 °C; ignores reactance, temperature rise and harmonics. Many codes recommend keeping drop within about 3–5 % — check the rules that apply to your installation.
  • Educational estimate. Electrical, structural and other safety-critical work must follow local codes and be checked by a qualified professional.

What this calculator does

Long or thin cables lose voltage, which can make equipment underperform and wastes energy as heat.

Formula and method

R = ρ × L ÷ A per conductor; ΔV = 2 × I × R (single-phase/DC) or √3 × I × R (three-phase); AWG area = π/4 × (0.127 mm × 92^((36 − n)/39))²

Worked example

Calculated by this tool with its default inputs:

Inputs

  • Conductor: Copper
  • Conductor size given as: Cross-section in mm²
  • Cross-section: 2.5 mm²
  • One-way cable length: 30 m
  • Load current: 16 A
  • Supply voltage: 230 V
  • Circuit: Single-phase or DC (two conductors)

Results

  • Voltage drop: 6.621 V
  • Drop as % of supply: 2.878%
  • Voltage at the load: 223.38 V
  • Conductor cross-section: 2.5 mm²
  • Power lost in the cable: 105.9 W

How to read the results

Compare the percentage drop with the limit in your wiring code.

Assumptions and limitations

  • Resistivity at 20 °C: copper 1.7241 × 10⁻⁸ Ω·m (IACS), aluminium 2.82 × 10⁻⁸ Ω·m; hot conductors have higher resistance.
  • Reactance is ignored, which is reasonable for small cables at power frequency.
  • Educational estimate. Electrical, structural and safety-critical work must follow local codes and be designed or checked by a qualified professional.

These are educational estimates. Electrical, structural and other safety-critical work must comply with local codes and be designed or checked by a qualified professional.

Questions

What is an acceptable drop?

Many codes and guides cite about 3 % for branch circuits and 5 % overall, but check yours.

Methodology and verification

Result type
Estimate based on the stated model and assumptions
Formula version
1.0
Automated verification
4 reference and validation test cases, checked against independently computed values. The site cannot be built if any of them fail.
Editorial review
Awaiting human editorial review. The explanation was drafted with AI assistance; the formula and examples are verified by the automated tests above.

Privacy

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