Extension Cable Voltage Drop Calculator

A voltage drop calculator for extension cable 220v home wiring showing lost volts and percentage. Use the free Extension Cable Voltage Drop Calculator below — enter your values and get instant results, right in your browser. Voltage drop (V) = 2 × length (m) × current (A) × resistance per meter. Drop % = drop ÷ 220 × 100. Voltage at load = 220 − drop. Example: 30 m of 2.5 mm² at 10A → 2 × 30 × 10 × 0.0073 = 4.38V (1.99%) → 215.6V at the load.

How to use the Extension Cable Voltage Drop Calculator

A long, thin extension cable can quietly starve your appliances — motors overheat, UPS units misbehave, and lights dim at the far end. This voltage drop calculator for extension cable 220v home wiring computes exactly how many volts are lost along the cable and what percentage that is, plus the voltage your appliance actually receives. If the drop exceeds 5%, the fix is simple: a thicker cable or a shorter run.

  1. Measure the one-way cable length in meters and enter it (the calculator doubles it for the live + neutral loop).
  2. Enter the load current in amps — watts ÷ 220, e.g. a 2200W heater draws 10A.
  3. Select your cable size from the dropdown (most home extensions are 1.5 or 2.5 mm²).
  4. Click Calculate to see the voltage drop in volts, the drop percentage, and the voltage at the far end.
  5. If the drop exceeds 5%, select the next thicker cable size and recalculate.

Formula

Voltage drop (V) = 2 × length (m) × current (A) × resistance per meter. Drop % = drop ÷ 220 × 100. Voltage at load = 220 − drop. Example: 30 m of 2.5 mm² at 10A → 2 × 30 × 10 × 0.0073 = 4.38V (1.99%) → 215.6V at the load.

Worked example

A 30-meter 1.5 mm² extension carries a 10A (2200W) load: drop = 2 × 30 × 10 × 0.0121 = 7.26V, which is 3.3% — the far end gets 212.7V, acceptable. But a 50-meter run of the same cable at 13A drops 15.7V (7.1%) leaving only 204V — motors will struggle, so upgrade to 2.5 mm² (4.3%) or 4 mm² (2.7%).

Frequently asked questions

Under 5% (11V on a 220V supply) is the common wiring-regulation limit; under 3% is recommended for motor loads like pumps and fridges, which overheat when starved of voltage.

Heat means the cable is undersized for the current — power lost as heat equals current² × resistance. A warm cable is wasting your electricity and is a fire risk; switch to a thicker cable or reduce the load.

Divide its watts by 220: a 2200W heater draws 10A, a 150W fridge about 0.7A running (but 4–5A at compressor start). Use the highest current the cable will carry.

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