How to use the cable voltage drop calculator
Find the voltage lost along a copper cable carrying a load over its length. Enter load current, one-way cable length, conductor cross-section, supply voltage in the fields above; the voltage drop are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “voltage drop calculator cable”, “cable voltage drop calculator”, “voltage drop in cable calculator”, “voltage drop on cable”, “wire size voltage drop”.
Formula
Variables
- I — Load current (A)
- L — One-way cable length (m)
- A — Conductor cross-section (mm²)
- V — Supply voltage (V)
Worked example
With load current = 20 A, one-way cable length = 30 m, conductor cross-section = 4 mm², supply voltage = 230 V, the calculator gives voltage drop ≈ 5.16 V; voltage drop ≈ 2.243478 %.
Tips for accurate results
- Enter the one-way cable length; the calculator doubles it for the return path.
- Check the result as a percentage of supply voltage against your local wiring rules.
- Use the calculator for copper cable; aluminium has about 1.5 times the resistance.
Common mistakes
- Entering the round-trip length and doubling it again.
- Applying this single-phase formula to a three-phase circuit, which needs a different factor.
- Ignoring the temperature effect on conductor resistance, which raises resistance on hot days.
Frequently asked questions
What is the cable voltage drop calculator used for?
Find the voltage lost along a copper cable carrying a load over its length. It helps with questions such as “voltage drop calculator cable”, “cable voltage drop calculator”, “voltage drop in cable calculator”.
What is the formula for the cable voltage drop calculation?
Voltage drop (V) = 2 × I × L × 1.72e-8 / (A × 1e-6). Voltage drop (%) = [Voltage drop] / V × 100. Here I is load current (A), L is one-way cable length (m), A is conductor cross-section (mm²), V is supply voltage (V).
What inputs do I need for the cable voltage drop calculator?
You need load current in A, one-way cable length in m, conductor cross-section in mm², supply voltage in V. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the cable voltage drop calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the cable voltage drop result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.