Microstrip Impedance Calculator

Every figure is computed on each run; this only chooses the headline result.
Steady-state DC or RMS current the conductor must carry.
Conductor rise above ambient. IPC-2221 charts cover 10, 20 and 30 degrees C.
Finished copper weight. 0.5, 1, 2 and 3 oz are the common classes.
Set a measured finished thickness in mils to override the weight-based value. 0 uses the weight.
Industry nominal is 1.37 mil (34.8 um) per oz/ft^2. Etch-back can leave outer layers ~0.2 mil thinner.
Used for the current-capacity, resistance and impedance results. Units follow the dimension unit below.
Conductor run length used for resistance, voltage drop and dissipation.
Conductor resistance is evaluated at ambient + temperature rise.
1.724e-8 ohm*m is 100% IACS annealed copper (NIST). Use 1.68e-8 for high-purity copper.
Alpha for annealed copper referred to 20 C.
FR-4 is about 4.2-4.5 at 1 GHz; Rogers RO4350B is 3.48. Take it from the laminate datasheet.
Prepreg/core thickness between the trace and its reference plane.
Total distance between the two reference planes enclosing the trace.
Width is back-solved to hit this single-ended impedance. 0 to skip.
Minimum trace width (IPC-2221)
11.895 mil
PCB Trace Width, Current and Impedance Calculator
Minimum trace width
0.3021 mm
Required cross-section
16.296 mil^2
Current capacity of the entered width
0.882 A
Copper thickness
1.370 mil
Copper thickness
34.80 um
Width used for resistance
11.895 mil
DC resistance at temperature
0.173646 ohm
Resistance per inch
44.1060 mohm/in
Voltage drop
0.1736 V
Power dissipated in the trace
0.1736 W
Conductor temperature
35.0 degC
Single-ended impedance
67.483 ohm
Differential impedance
104.910 ohm
Propagation delay
139.992 ps/in
Propagation delay
5.5115 ps/mm
Delay of this trace length
551.15 ps
Capacitance per inch
2.0745 pF/in
Inductance per inch
9.4470 nH/in
Width for the target impedance
17.219 mil
Width for the target impedance
0.4374 mm
Geometry evaluated
surface microstrip
Worked out from IPC-2221B/C, Generic Standard on Printed Board Design, conductor current-carrying capacity (I = k dT^0.44 A^0.725) and 4 other sources.
IPC-2221 conductor sizing is a conservative chart fit and IPC-2152 supersedes it for production current-capacity work. Have conductor sizing for safety-critical, high-current or high-voltage designs reviewed by a qualified PCB engineer against the applicable IPC standard and any product safety standard (e.g. IEC 62368-1) before release.

How this is worked out

10 steps
  1. Copper thickness = 1.37 mil (34.8 um)
  2. IPC-2221 area: A = (I / (k * dT^0.44))^(1/0.725) = (1 / (0.048 * 2.754229))^1.37931 = 16.296 mil^2
  3. Minimum width = A / thickness = 16.296 / 1.37 = 11.8949 mil (0.3021 mm)
  4. Capacity of a 10 mil trace: I = 0.048 * 10^0.44 * 13.7^0.725 = 0.8818 A
  5. R(20 C) = rho * L / A = 1.724e-8 * 0.1 / 1.051353e-8 = 0.1639792 ohm
  6. R(35 C) = R20 * (1 + 0.00393 * (35 - 20)) = 0.17364578 ohm; drop = 0.17365 V, dissipation = 0.17365 W
  7. Microstrip Z0 = (87/sqrt(4.3+1.41)) * ln(5.98*10 / (0.8*10 + 1.37)) = 67.483 ohm
  8. Differential Z = 2*Z0*(1 - 0.48*exp(-0.96*s/h)) with s = 8 mil gives 104.91 ohm
  9. Propagation delay = 139.992 ps/in (5.5115 ps/mm); Z0 = tpd/C gives 2.0745 pF/in and 9.447 nH/in
  10. Width solved for 50 ohm: 17.219 mil (0.4374 mm)

Results are general information, not financial, tax, legal, medical or engineering advice.