DC Wire Voltage Drop Calculator
Estimate DC conductor voltage drop, load voltage and wire heating, or solve the conductor area for a chosen drop limit using an entered operating resistivity.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Calculate series conductor resistance from operating resistivity, total current path length and cross-sectional area. Apply Ohm’s law for voltage loss and I²R for conductor power loss. Rearrange to solve the area for a chosen voltage-drop limit.
R=ρLtotal/A; ΔV=IR; loss=I²R; required A=IρLtotal/(supply×limit/100)
Worked example
For 12 V, 5 A, a 5 m one-way run with equal return, 2.5 mm² area and resistivity 0.0175 ohm mm²/m: R=0.07 ohm, drop=0.35 V, loss=1.75 W and load voltage=11.65 V.
Assumptions and input details
Two-conductor DC resistance model with equal outbound/return areas. The one-way option doubles length; total-length mode does not. Enter resistivity at the actual operating temperature; the default is an illustrative input, not a material certificate. Contacts, connectors, source impedance and AC reactance are excluded. Constant current is entered independently; combinations needing a wire drop above the supply are rejected. Solved area is a theoretical minimum for voltage drop only, not a standard cable size or an ampacity, temperature-rise, fault-protection or code-compliance determination. No country wiring rules are assumed.
References: Fluke voltage-drop explanation
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
SI prefixes are explicit: for example, milli means one thousandth, micro one millionth and kilo one thousand. Changing a unit changes the interpretation of the entered number.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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