Voltage Drop Calculator.

Formula and practical context.

Variables and method

I is amperes, L is one-way feet, and R is ohms per 1,000 feet. The calculation is single phase: 2 × I × L × R/1000; three phase: √3 × I × L × R/1000. Voltage drop is an estimate of conductor loss under the stated current and resistance. Keep the labels and units together while checking the arithmetic. Record the entered values before comparing alternatives, retain extra digits until the final display, and use the result as a transparent planning value rather than an instruction. Write down the assumption that most affects this particular result, then test a conservative alternative before relying on it.

Numeric worked example

At 10 A, 100 ft, and 1.24 Ω per 1,000 ft, single-phase drop is 2.48 V. Substitute values only after confirming compatible units and signs. Work through the intermediate operation, then round the displayed answer rather than each input. Keep the labels and units together while checking the arithmetic. Record the entered values before comparing alternatives, retain extra digits until the final display, and use the result as a transparent planning value rather than an instruction. Write down the assumption that most affects this particular result, then test a conservative alternative before relying on it.

Interpret the result

For Voltage Drop Calculator, Voltage drop is an estimate of conductor loss under the stated current and resistance. A mathematically correct number answers the stated question only; it does not automatically establish suitability, safety, or policy compliance. Keep the labels and units together while checking the arithmetic. Record the entered values before comparing alternatives, retain extra digits until the final display, and use the result as a transparent planning value rather than an instruction. Write down the assumption that most affects this particular result, then test a conservative alternative before relying on it.

Edge cases and validation

Resistance changes with conductor material, temperature, connections, and actual route length. Blank fields, non-finite values, and unsafe magnitudes receive an explicit message instead of a silent fallback. Keep the labels and units together while checking the arithmetic. Record the entered values before comparing alternatives, retain extra digits until the final display, and use the result as a transparent planning value rather than an instruction. Write down the assumption that most affects this particular result, then test a conservative alternative before relying on it.

Limits of this estimate

Electrical design must follow the applicable code and a qualified designer. Check the governing document or qualified source before acting on a consequential result. Keep the labels and units together while checking the arithmetic. Record the entered values before comparing alternatives, retain extra digits until the final display, and use the result as a transparent planning value rather than an instruction. Write down the assumption that most affects this particular result, then test a conservative alternative before relying on it.

Check the assumptions.

Electrical design must follow the applicable code and a qualified designer.

NEC overview (NFPA)