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Voltage Drop Calculator

Enter Wire material, Wire size, One-way length, Voltage in volts, and Current in amps, then press Calculate for the voltage drop and wire resistance.

What the calculator does

Select Wire material from Copper, Aluminum, Carbon steel, Electrical steel, Gold, Nichrome, Nickel, or Silver, or enter Resistivity (Ω·m). Choose Diameter unit (AWG, inch, or mm), Wire size, Length unit (feet or meters), One-way length, Current type (DC, AC - Single phase, or AC - Three phase), Voltage in volts, and Current in amps.

The form computes only when the button is pressed. Results appear in three cards below the button: Voltage drop, Percentage of voltage drop, and Wire resistance. Copy writes a result and its unit to the clipboard. Clear resets the form. Everything runs in the browser and nothing is uploaded.

Voltage drop formula

For DC and AC single-phase circuits, the tool computes V_drop = I × R. For example, with Copper, Diameter unit: AWG, Wire size: 12, Length unit: feet, One-way length: 50, Current type: DC, Voltage in volts: 120, and Current in amps: 10, the expression is V_drop = I × R = 10 A × 0.15881271385951 Ω ≈ 1.5881271385951 V, with Percentage of voltage drop: 1.32343928216258 % and Wire resistance: 0.15881271385951 Ω.

For AC three-phase circuits, the formula is V_drop = 1.732 / 2 × I × R. With Current type: AC - Three phase and the same 12 AWG copper run at 50 feet, 120 volts, and 10 amps, the expression is V_drop = 1.732 / 2 × I × R = 1.732 / 2 × 10 A × 0.15881271385951 Ω ≈ 1.37531810202336 V, giving Percentage of voltage drop: 1.1460984183528 %.

With Aluminum, Diameter unit: mm, Wire size: 2.5, Length unit: meters, One-way length: 20, Current type: AC - Single phase, Voltage in volts: 240, and Current in amps: 16, V_drop = I × R = 16 A × 0.229794273033802 Ω ≈ 3.67670836854083 V, with Percentage of voltage drop: 1.53196182022535 % and Wire resistance: 0.229794273033802 Ω.