Voltage Drop and IR Drop Calculator
Calculate DC voltage drop from a known path resistance, or derive conductor resistance from material resistivity, length, and cross-sectional area.
Inputs and tolerances
Calculate drop from a known path resistance, or derive resistance from conductor geometry and material resistivity.
902.5m to 1.103V
Known-resistance mode uses the complete path resistance directly, so any return-path or connector resistance should already be included.
Nominal results and guaranteed range
Estimate DC voltage drop before routing a power path
Use this calculator for cable voltage drop, wire voltage drop, PCB power-path drop, connector resistance checks, and first-pass IR-drop estimates. It supports both a direct resistance entry and a conductor-geometry mode for material, length, and cross-sectional area.
Known resistance
Use measured, simulated, or supplier-provided path resistance directly.
Conductor geometry
Derive resistance from material resistivity, length, and cross-sectional area.
Target-drop sizing
Estimate allowable current, maximum resistance, required area, or maximum length for a selected drop limit.
Equations and assumptions
Geometry mode uses the same resistance, voltage-drop, and power-loss engine as direct-resistance mode. One-way length is doubled to include the return path; round-trip length is used as entered.
Known resistance drop
Vdrop = I × R
Use when the complete path resistance is known or measured.
Conductor resistance
R = ρ × L / A
Use geometry mode to derive resistance from resistivity, effective length, and cross-sectional area.
Power loss
Ploss = I² × R
Estimate heat in the conductor, cable, connector, or PCB power path.
Load voltage
Vload = Vsource - Vdrop
Use the optional source-voltage input to estimate the voltage remaining at the load.
Target-drop sizing
Rmax = Vtarget / I
Use the optional target-drop input to estimate allowable current, maximum path resistance, and geometry sizing limits.
Length and material notes
One-way versus round-trip
A load current needs an outbound and return path. Select one-way length when you enter only the physical run from source to load; select round-trip when the complete current-loop length is already included.
Resistivity is approximate
The built-in copper, aluminium, silver, and gold values are room-temperature first-pass values. Alloy, temperature, plating, and manufacturing tolerance can move the real result.
Related calculators and guides
AWG wire gauge converter
Convert AWG sizes to conductor diameter and area before using geometry mode.
Ohm's Law calculator
Check the V = I × R relationship behind the voltage-drop result.
Resistor power calculator
Review dissipation, wattage margin, and thermal derating for resistive paths.
PCB trace current and voltage-drop guide
Review trace current, voltage drop, temperature rise, and board-level assumptions.