Voltage Drop Calculator

Q: What is the formula for voltage drop?

The basic formula for voltage drop is V = I × R, where V is voltage drop, I is current in amps, and R is wire resistance in ohms.

Q: Is 4% voltage drop acceptable?

Ideally, voltage drop should not exceed 3%. Anything above 5% can cause performance loss or damage to sensitive equipment.

Q: What is the voltage drop per 100 feet?

It depends on wire gauge and current. For example, a 12 AWG copper wire carrying 15A loses about 0.048V per foot, or 4.8V per 100 feet.

Q: What is Ohm’s law for voltage drop?

Ohm’s law states that voltage drop equals current multiplied by resistance (V = I × R).

Use our Voltage Drop Calculator to determine voltage loss in your electrical circuit based on wire gauge (AWG), load current, and one-way distance. Ideal for electricians, engineers, solar installers, and DIY projects.

How to Calculate Voltage Drop

Voltage drop occurs when current flows through a conductor and some energy is lost as heat. Keeping this drop under 3% ensures proper performance of electrical systems.

V_drop = I × R

Example

For a 120V circuit carrying 15A through 12 AWG wire over 50 ft:

Resistance = (1.588 / 1000) × 50 × 2 = 0.1588 Ω
Vdrop = 15 × 0.1588 = 2.38 V
Voltage drop = 1.98%

Acceptable Voltage Drop Limits

Type	Max Drop (%)
Lighting Circuit	3%
Main Feeder	2%
Total Combined	5%

FAQs about Voltage Drop

What is the formula for voltage drop?

The formula is V = I × R.

Is 4% voltage drop acceptable?

For most systems, voltage drop should be ≤3%. Anything above 5% is excessive.

What is the voltage drop per 100 feet?

It depends on the wire gauge and current load — 12 AWG carrying 15A loses about 4.8V per 100 feet.

What is Ohm’s law for voltage drop?

Ohm’s law defines voltage drop as V = I × R.