PCB Trace Width Calculator
PCB trace width from current, copper weight and temperature rise by the IPC-2221 formula, in mils and mm, plus the trace resistance and voltage drop. How it works
Use the PCB Trace Width Calculator
About the PCB Trace Width Calculator
A 1 A current on an outer layer of 1 oz copper with a 10 °C temperature rise needs a trace about 11.83 mils (0.300 mm) wide by the IPC-2221 formula. On an inner layer the same trace needs 30.76 mils (0.781 mm), because buried copper sheds heat less well. Give the trace length and the calculator also shows its resistance, voltage drop and power loss: 50 mm of the 0.300 mm trace is 83.1 mΩ, which drops 83.1 mV at 1 A.
Outer layer trace width at a 10 °C rise
| Current | 0.5 oz copper | 1 oz copper | 2 oz copper | 3 oz copper |
|---|---|---|---|---|
| 0.5 A | 0.231 mm (9.09 mils) | 0.115 mm (4.55 mils) | 0.058 mm (2.27 mils) | 0.038 mm (1.52 mils) |
| 1 A | 0.601 mm (23.65 mils) | 0.300 mm (11.83 mils) | 0.150 mm (5.91 mils) | 0.100 mm (3.94 mils) |
| 2 A | 1.563 mm (61.53 mils) | 0.781 mm (30.76 mils) | 0.391 mm (15.38 mils) | 0.260 mm (10.25 mils) |
| 3 A | 2.734 mm (107.64 mils) | 1.367 mm (53.82 mils) | 0.683 mm (26.91 mils) | 0.456 mm (17.94 mils) |
| 5 A | 5.531 mm (217.75 mils) | 2.765 mm (108.88 mils) | 1.383 mm (54.44 mils) | 0.922 mm (36.29 mils) |
| 10 A | 14.388 mm (566.46 mils) | 7.194 mm (283.23 mils) | 3.597 mm (141.62 mils) | 2.398 mm (94.41 mils) |
IPC-2221 formula with k = 0.048, as the calculator computes it. Widths below 0.01 mils or 0.001 mm print as less than that figure. The 10 A, 0.5 oz cell is wider than 400 mils, beyond the range of the IPC-2221 graphs (up to 35 A, 400 mils, 10 to 100 °C rise, 0.5 to 3 oz), so the formula extrapolates there and the figure is a rough estimate.
Inner layer trace width at a 10 °C rise
| Current | 0.5 oz copper | 1 oz copper | 2 oz copper | 3 oz copper |
|---|---|---|---|---|
| 0.5 A | 0.601 mm (23.65 mils) | 0.300 mm (11.83 mils) | 0.150 mm (5.91 mils) | 0.100 mm (3.94 mils) |
| 1 A | 1.563 mm (61.53 mils) | 0.781 mm (30.76 mils) | 0.391 mm (15.38 mils) | 0.260 mm (10.25 mils) |
| 2 A | 4.066 mm (160.06 mils) | 2.033 mm (80.03 mils) | 1.016 mm (40.02 mils) | 0.678 mm (26.68 mils) |
| 3 A | 7.112 mm (280.01 mils) | 3.556 mm (140.01 mils) | 1.778 mm (70.00 mils) | 1.185 mm (46.67 mils) |
| 5 A | 14.388 mm (566.46 mils) | 7.194 mm (283.23 mils) | 3.597 mm (141.62 mils) | 2.398 mm (94.41 mils) |
| 10 A | 37.430 mm (1473.62 mils) | 18.715 mm (736.81 mils) | 9.357 mm (368.41 mils) | 6.238 mm (245.60 mils) |
IPC-2221 formula with k = 0.024, as the calculator computes it. The 5 A and 10 A cells at 0.5 oz and the 10 A cell at 1 oz are wider than 400 mils, beyond the range of the IPC-2221 graphs, so the formula extrapolates there and those figures are rough estimates.
Effect of the allowed temperature rise on 3 A, 1 oz, outer layer
| Temperature rise | Trace width |
|---|---|
| 10 °C | 1.367 mm (53.82 mils) |
| 20 °C | 0.898 mm (35.34 mils) |
| 30 °C | 0.702 mm (27.63 mils) |
Resistance, voltage drop and power loss of a 100 mm trace (outer layer, 1 oz, 10 °C rise)
| Current | Trace width | Resistance | Voltage drop | Power loss |
|---|---|---|---|---|
| 0.5 A | 4.55 mils (0.115 mm) | 432.5 mΩ | 216.2 mV | 108.1 mW |
| 1 A | 11.83 mils (0.300 mm) | 166.2 mΩ | 166.2 mV | 166.2 mW |
| 2 A | 30.76 mils (0.781 mm) | 63.9 mΩ | 127.8 mV | 255.6 mW |
| 3 A | 53.82 mils (1.367 mm) | 36.5 mΩ | 109.6 mV | 328.8 mW |
| 5 A | 108.88 mils (2.765 mm) | 18.1 mΩ | 90.3 mV | 451.4 mW |
| 10 A | 283.23 mils (7.194 mm) | 6.94 mΩ | 69.4 mV | 694.1 mW |
Each trace is the IPC-2221 width for its current, so a higher current gets a wider trace and a lower drop. Copper resistivity 1.68 × 10⁻⁸ Ω·m at 20 °C with a temperature coefficient of 0.00404 per °C (Wikipedia’s resistivity table), taken at 30 °C: 20 °C plus the allowed rise.
How to use this tool
- Enter the current in amps and the temperature rise you allow in °C.
- Choose the copper weight (0.5, 1, 2 or 3 oz) and the layer, outer or inner.
- Enter the trace length in mm or inches for its resistance, voltage drop and power loss.
- Enter the ambient temperature if the board runs warmer or colder than 20 °C. It changes the resistance, not the width.
- Read the width for your layer in mils and mm, with the other layer’s width beside it, then check it against your board manufacturer’s rules.
Frequently asked questions
- How wide should a PCB trace be for 1 A?
- On an outer layer of 1 oz copper with a 10 °C rise, 11.83 mils (0.300 mm). On an inner layer, 30.76 mils (0.781 mm). With 2 oz copper the outer width halves to 5.91 mils (0.150 mm).
- Why are inner-layer traces wider than outer ones?
- The IPC-2221 constant k is 0.048 for outer layers and 0.024 for inner layers, because inner copper loses heat less well. Halving k makes the trace about 2.60 times wider, so 11.83 mils becomes 30.76 mils.
- How does the allowed temperature rise change the width?
- A larger rise allows a narrower trace. For 3 A on 1 oz outer copper the width is 53.82 mils at a 10 °C rise, 35.34 mils at 20 °C and 27.63 mils at 30 °C.
- Should I use IPC-2221 or IPC-2152?
- IPC-2152, released in 2009, replaces the conductor sizing charts of IPC-2221 and adds the effect of nearby planes, board thickness and material. This calculator uses the IPC-2221 formula, which is a fit to test boards with no nearby copper. For boards with planes it is conservative, so a design checked against IPC-2152 may allow a narrower trace.
- What does 1 oz copper mean for the calculation?
- Copper weight is given in ounces per square foot. The calculator uses a thickness of 1.378 mils for each ounce, about 35 µm, so 1 oz copper is 1.378 mils thick and 2 oz is 2.756 mils.
- What is the resistance of a PCB trace?
- R = ρ × length ÷ (width × thickness). The calculator uses copper at 1.68 × 10⁻⁸ Ω·m at 20 °C, raised 0.404% per °C above that, at the ambient temperature (20 °C unless you type one) plus the allowed rise. A 1 A trace on 1 oz outer copper at a 10 °C rise, 50 mm long, is 83.1 mΩ: it drops 83.1 mV and turns 83.1 mW into heat. At a 40 °C ambient the same trace is 89.6 mΩ. On 2 oz copper the suggested trace is half as wide and twice as thick, so the resistance is the same 83.1 mΩ.
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