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Browse 8 power tools. Opening Residential AC Voltage Drop Calculator.

Watts to AmpsConvert electrical power (watts) to current (amps) at a given voltage.Use this to check a device won't overload your circuit or blow a fuse.
Amps to WattsConvert current (amps) and voltage into power (watts).Use this to figure out how much power your gear draws and what it costs to run.
Residential AC Voltage Drop CalculatorCalculate AC voltage drop in home wiring from supply voltage, amps, cable length (m), and AWG or mm² copper size.Use this to make sure far-away outlets still deliver full voltage to your devices.
Ohm's Law CalculatorFind voltage, current, or resistance when you know any two values (V = I × R).Use this to fill in the missing electrical value for any circuit you're working on.
Volts to Watts CalculatorConvert voltage and current into electrical power in watts.Use this to work out the real power of any device from its label values.
Watts to Volts CalculatorFind voltage from power and current (V = W ÷ A).Use this to check what voltage your setup needs to deliver the power you want.
Power Factor CalculatorCalculate power factor from real power (kW) and apparent power (kVA).Use this to see how efficiently your equipment uses power and avoid utility penalties.
AC Inrush Current Limit CalculatorFind nominal amps, peak motor inrush, and recommended breaker size with B/C/D curve guidance.Use this to pick a breaker that won't trip every time your motor starts.

Residential AC Voltage Drop Calculator

Inputs

Adjust values to update results live

Supply voltage (V)

Line-to-neutral (120 V) or line voltage (230 V) for your circuit

Load current (A)

Voltage drop

Enter voltage, amps, length & wire size

Voltage at load

Enter values above

Drop percentage

Enter values above

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How to use the Residential AC Voltage Drop Calculator

The Formula

Long or undersized copper runs add resistance. Loads see less than nominal voltage—motors overheat, chargers throttle, and lights dim. Most guides target ≤3% drop on branch circuits and ≤5% total feeder plus branch.

Practical Example

Drop (V) = current (A) × resistance × 2 (out-and-back) × one-way length (m). Drop % = 100 × drop ÷ supply voltage. Uses typical copper Ω/m at 20 °C for AWG or mm².

About Residential AC Voltage Drop Calculator

Drop (V) = current (A) × resistance × 2 (out-and-back) × one-way length (m). Drop % = 100 × drop ÷ supply voltage. Uses typical copper Ω/m at 20 °C for AWG or mm².

Pick the conductor you are installing. Metric installs use mm²; North American branch wiring often lists AWG. When in doubt, size up one step for continuous loads (EVSE, HVAC, heat pump).

Q: 120 V or 240 V? A: Use the voltage the load actually sees (usually 120 V line-to-neutral in US branch circuits). Q: Power factor? A: This is a resistive planning estimate—inductive motor starts may need larger wire. Q: Aluminum wire? A: Copper only here; AL needs larger area.

Related tools

Watts to AmpsConvert electrical power (watts) to current (amps) at a given voltage.Use this to check a device won't overload your circuit or blow a fuse.
DC Cable Size CalculatorRecommend DC wire gauge from current, one-way length, and system voltage.Use this to pick a wire gauge that's safe and doesn't waste power.
Battery Voltage Drop CalculatorEstimate DC wire voltage drop and voltage at the load from amps, length, and system voltage.Use this to keep your wiring short and thick enough so devices get full power.
Amps to WattsConvert current (amps) and voltage into power (watts).Use this to figure out how much power your gear draws and what it costs to run.

How to use the Residential AC Voltage Drop Calculator

The Formula

Practical Example

Drop (V) = current (A) × resistance × 2 (out-and-back) × one-way length (m). Drop % = 100 × drop ÷ supply voltage. Uses typical copper Ω/m at 20 °C for AWG or mm².

About Residential AC Voltage Drop Calculator

Drop (V) = current (A) × resistance × 2 (out-and-back) × one-way length (m). Drop % = 100 × drop ÷ supply voltage. Uses typical copper Ω/m at 20 °C for AWG or mm².

Pick the conductor you are installing. Metric installs use mm²; North American branch wiring often lists AWG. When in doubt, size up one step for continuous loads (EVSE, HVAC, heat pump).

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