Pcb Trace Resistance Calculator - Resistance, Drop, and Heat

A PCB trace resistance calculator is a board-design tool that turns the geometry of a copper trace into a usable resistance value. You give it the trace length, width, and thickness, set the operating temperature, and it returns the DC resistance of the segment, the resistance normalised to a one-metre run, and the voltage drop you can expect at a chosen current. The same calculator doubles as a copper trace calculator by default and can be retargeted at silver, gold, or aluminum when a board uses a plated finish or a different base metal.

• • Sizing a power-distribution trace: Check whether a candidate width and copper weight keep the voltage drop under a target percentage of the supply rail.
• • Estimating heat in a high-current segment: Combine the resistance and the planned current to predict the I²R heating and confirm the trace stays within the published temperature-rise budget.
• • Comparing copper weights on the same board: Switch from 1 oz/ft² to 2 oz/ft² copper (35 µm to 70 µm) to see how the resistance and the voltage drop change.

The calculator covers the rectangular trace approximation: cross-section is the trace width times the trace thickness, valid whenever the width is much larger than the thickness (the usual case on a printed board). For non-rectangular traces, the same R = ρ × L / A form applies once the equivalent cross-sectional area is known, and the electrical resistance calculator solves the same uniform-conductor equation with general length and area inputs. According to the Copper Development Association, copper is the standard benchmark for electrical conductivity, conducts better than any other metal except silver, and is the dominant material used in printed-circuit boards.

The calculator uses the textbook Ohm's Law form for the resistance of a uniform conductor, then folds in a linear temperature correction so the result matches the trace at its operating temperature. The same resistance feeds the voltage drop helper, so the two values always agree.

• L, W, T: Trace length, width, and thickness. Entered in mm / mm / µm and converted to metres inside the calculation.
• T_amb: Ambient temperature of the board, used with the 20 °C reference and α.
• ρ, α: Bulk resistivity and linear temperature coefficient at 20 °C. Copper defaults to 1.72 × 10⁻⁸ Ω·m and 0.00393 1/°C; silver, gold, and aluminum are also preset.

Once the resistance is known, the voltage drop is just Ohm's Law (V = I × R) at the current you set, and the same value flows into a per-metre figure so different segments compare on equal terms. The Engineering Toolbox resistivity reference lists copper at 1.724 × 10⁻⁸ Ω·m at 20 °C with a temperature coefficient of 3.93 × 10⁻³ 1/°C, the pair the calculator rounds to for the copper preset.

According to Engineering Toolbox resistivity reference, copper has a bulk resistivity of 1.724 × 10⁻⁸ Ω·m at 20 °C with a temperature coefficient of 3.93 × 10⁻³ 1/°C, and silver has the lowest resistivity in the table at 1.59 × 10⁻⁸ Ω·m.

Four small ideas explain every number the calculator returns.

These four ideas cover everything the calculator returns. When a layout calls for a non-copper finish, the same cross-section and length feed the formula; only the bulk resistivity and the temperature coefficient change, which is why the material preset exposes overrides for both. For non-rectangular traces - curved pours, irregular polygons, busses with cutouts - the equivalent area in the denominator has to be solved first, and the cross-sectional area calculator handles those shapes so the resistance result reflects the real conductor geometry.

Five short steps take a layout drawing all the way to a resistance and voltage drop value.

1. 1 Measure the trace geometry: Pull the length, width, and copper weight from the layout. Convert copper weight to thickness: 1 oz/ft² ≈ 35 µm, 0.5 oz/ft² ≈ 17.5 µm, 2 oz/ft² ≈ 70 µm.
2. 2 Pick the operating temperature: Use the board's ambient temperature inside the enclosure, not the room temperature. Hot enclosures push the real number well above 25 °C.
3. 3 Choose the trace material: Stay on Copper for standard boards. Switch to Silver, Gold, or Aluminum when the board uses a plated finish. Choose Custom to enter your own resistivity and temperature coefficient.
4. 4 Set the current for the voltage drop helper: Enter the steady-state current the trace is expected to carry. Leave at 1 A if you only want a per-amp drop and plan to multiply by your real current later.
5. 5 Read the result panel: The result panel shows the resistance, the resistance per metre, the voltage drop at the current you set, and the cross-sectional area.

For a 50 mm long, 0.25 mm wide 1 oz copper trace carrying 0.5 A at 35 °C ambient, enter length = 50, width = 0.25, thickness = 35, ambient = 35, material = Copper, current = 0.5. The calculator returns about 0.103 Ω, 2.05 Ω/m, and a 0.051 V drop at 0.5 A. To see how that drop stacks up against the rest of the supply path, feed the trace and load resistances into the voltage divider calculator, which models them as a series pair.

A purpose-built PCB trace resistance calculator keeps the geometry, the material, and the temperature in one place so the numbers stay consistent across a layout review.

• • Resistive losses visible in one screen: The result panel shows resistance, voltage drop, and per-metre ohms at the same time, so a designer can see the impact of width or copper weight without re-running the calculation.
• • Temperature-corrected by default: The ambient temperature feeds the linear temperature correction, so the result reflects the real operating point instead of a 20 °C textbook value.
• • Material presets with safe overrides: Copper, silver, gold, and aluminum are exposed as one-click presets. Custom lets you enter your own resistivity and temperature coefficient for unusual finishes without rewriting the formula.
• • Cross-section sanity check: The cross-sectional area readout confirms the geometric area used in the calculation, so a typo in width or copper weight is visible in the result panel.
• • Ohm's Law built in: The voltage drop helper multiplies the resistance by the current you set, so the same value backs both numbers and there is no risk of a miscalculated V = I × R.

When the load is specified in watts rather than amps, the voltage drop helper needs the current, not the power. Convert the load with the watts to amps converter at the supply voltage, then paste that current into this calculator's Current input to read the trace voltage drop alongside the resistance.

Three variables drive the resistance, and two limitations tell you when to reach for a different tool.

• • The calculator uses the rectangular cross-section approximation, which assumes the trace width is much larger than the thickness. For unusual shapes such as tapered or coaxial cross-sections, the area has to be computed by hand.
• • The linear temperature correction is valid across the practical PCB range but underestimates the change at very low or very high temperatures, where the resistivity of copper becomes non-linear.

For high-current traces, the I²R loss feeds a thermal-rise estimate: combine the dissipated power with the copper mass to project a steady-state temperature change. The specific heat calculator takes the copper mass and the watt number from V × I to estimate the temperature rise for a given load. According to the Global Electronics Association IPC standards catalog, the IPC-2152 series maps trace width, copper weight, and ambient temperature to the current a trace can carry without exceeding a target temperature rise, using the same cross-section this calculator prints.