Inputs
- Trace length
- Trace width
- Copper thickness
- Current
- Copper temperature
FPC / PCB Engineering Calculator
PCB Power Calculator: Trace Resistance & Voltage Drop
Calculate PCB trace resistance, voltage drop and power loss from trace length, width, copper thickness, current and operating temperature.
How to use the PCB Power / Trace Resistance Calculator
Trace resistance and voltage drop matter for power paths, LEDs, motors, sensors and low-voltage high-current circuits. This calculator estimates resistance, voltage drop and power loss from conductor geometry.
Trace resistance, voltage drop and power loss
Formula: R = rho x L / A; Vdrop = I x R; P = I x Vdrop = I^2 x R
- R: conductor resistance.
- rho: copper resistivity adjusted for temperature.
- L: trace length.
- A: cross-sectional area from trace width and copper thickness.
- Vdrop: voltage drop along the trace.
- P: power dissipated as heat in the conductor.
Formula Basis
- Formula basis: conductor resistance from resistivity, length and cross-sectional area, combined with Ohm's law.
- Reference: OpenStax University Physics electrical power relations include P = IV and P = I^2R. https://openstax.org/books/university-physics-volume-2/pages/9-5-electrical-energy-and-power
- Engineering note: use finished copper thickness and expected operating temperature for closer production estimates.
Example
A 100 mm long, 0.2 mm wide, 35 um copper trace carrying 1 A has roughly 246 mOhm resistance at 20 degC.
Outputs
- Trace resistance
- Voltage drop
- Power loss
- mV per amp
Engineering Notes
- Long and narrow traces can create meaningful voltage drop even when current capacity appears acceptable.
- Copper resistance increases with temperature, so hot operating conditions should be reviewed.
- For dynamic FPC areas, avoid solving voltage drop by abrupt width changes in bend zones.
Validation Checks
- Voltage drop budget
- Power loss
- Thermal rise
- Current path width
Related Manufacturing Process
- Circuit Layout - Trace width, spacing, bend-zone routing, differential pair spacing
- Electrical Test - Open / short, resistance, voltage drop, impedance coupon
Related Calculators
- PCB Trace Width Current Calculator - Estimate PCB trace width and current capacity from copper thickness and temperature rise.
- PCB Impedance Calculator / Impedance Planner - Early PCB impedance calculator for single-ended and differential routing planning.
- Creepage and Clearance / Voltage Spacing Calculator - Estimate creepage and clearance spacing from a user-defined voltage rule before formal standard review.
FAQ
Why is this different from trace current capacity?
Current capacity estimates temperature rise. Resistance calculation estimates electrical loss and voltage drop. Both should be checked for power conductors.
Does plating copper reduce resistance?
Yes. Finished copper thickness increases cross-sectional area and reduces resistance, so use finished copper thickness when available.