pcb trace inductance calculator

Estimate the partial self-inductance of a straight PCB trace using a common rectangular-conductor approximation.

Trace Length (mm)

Trace Width (mm)

Copper Thickness (µm)

Frequency (MHz, for reactance)

Enter values and click Calculate.

Formula used: L(nH) = 0.2·l·[ln(2l/(w+t)) + 0.2235((w+t)/l) + 0.5], where l, w, t are in mm.

What this calculator does

This PCB trace inductance calculator gives you a quick estimate of how much inductance a straight copper trace contributes in a high-speed or power design. Even a few nanohenries can matter: it can increase ringing, worsen EMI, and create unexpected voltage spikes when current changes quickly.

The result is most useful during early layout decisions: trace length planning, switching node cleanup, return path strategy, and rough impedance sanity checks. For final signoff, field solver tools and measurement are still best.

How to use it

Enter the trace length in millimeters.
Enter the trace width in millimeters.
Enter copper thickness in micrometers (35 µm is typical 1 oz copper).
Optionally enter frequency to calculate inductive reactance (X_L).
Click Calculate to get total inductance and inductance per mm.

Why PCB trace inductance matters

1) Fast digital edges

In modern digital systems, edge rates are often much faster than clock frequency suggests. A “short” trace can still behave inductively during transitions. That added L interacts with parasitic C, often creating overshoot, undershoot, and ringing.

2) Switching power supplies

In buck, boost, and flyback layouts, high di/dt loops are extremely sensitive to stray inductance. Extra nanohenries in hot loops can generate large voltage spikes by V = L·di/dt, stressing MOSFETs and increasing conducted/radiated noise.

3) Analog and RF integrity

Trace inductance can degrade amplifier stability, alter filter behavior, and detune RF matching. Keeping current loops tight and return paths close is often as important as choosing the right components.

Interpreting the result

The calculator returns:

Total trace inductance in nH
Inductance per millimeter in nH/mm
Inductive reactance at the entered frequency in ohms

As a rule of thumb, longer and narrower traces produce more inductance. Increasing width helps, but reducing loop area and improving return path proximity are often even more effective at system level.

Design tips to reduce unwanted inductance

Keep high di/dt current paths short.
Route over a continuous ground plane whenever possible.
Avoid broken return paths (splits, voids, long detours).
Use wider copper for critical current paths.
Place decoupling capacitors close to IC power pins and vias.
Use paired vias for signal/return transitions between layers.

Practical limitations

This tool estimates partial self-inductance of a straight segment. Real PCB behavior also depends on:

Mutual coupling to nearby traces and planes
Trace bends, via transitions, and connectors
Dielectric stackup and return path geometry
Frequency-dependent effects and current distribution

For precision RF, high-speed serial links, or compliance-critical power stages, use 2D/3D EM extraction and validate with lab measurements.

Quick example

A 50 mm long trace, 0.25 mm wide, 35 µm thick, at 100 MHz often lands around a few dozen nH in this approximation. At that frequency, reactance can be significant enough to affect transient behavior and noise, especially in switching edges.

Bottom line

PCB trace inductance is small in absolute terms but huge in effect when currents change fast. Use this calculator to make layout choices early, reduce risk, and move faster toward a stable, low-noise design.