Calculation Methodology, Limits and Corrections

This page states exactly what the calculators compute, which inputs they accept, what they refuse to compute, and how to recompute the examples yourself. It is a record of the site's own models, not a certification and not a substitute for the standards or your fabricator's rules.

1. Trace width and current (IPC-2221 power law)

The trace width and via-current calculators use the empirical relation published in IPC-2221 for current versus temperature rise and cross-section:

I = k · ΔT^0.44 · A^0.725 (I in A, ΔT in °C, A = cross-section in mil²)
k = 0.048 for external layers, k = 0.024 for internal layers

Copper thickness is taken as 1.37 mil per oz/ft² (34.8 µm), so width = A ÷ (oz × 1.37). Resistance uses copper resistivity 1.724×10⁻⁸ Ω·m scaled by (1 + 0.00393·ΔT).

Input limits enforced by the page: current 0.01–50 A, temperature rise 1–100 °C, copper 0.25–6 oz. Values outside those limits are rejected with a message rather than extrapolated silently.

Test vectors you can recompute

Solve the relation above for A, then divide by the copper thickness. These four rows were recomputed independently of the site code with a short script (Python standard library only).

IPC-2221 test vectors
Current	Rise	Copper	Layer	Cross-section	Width
1 A	10 °C	1 oz	External	16.30 mil²	11.89 mil (0.302 mm)
5 A	10 °C	1 oz	External	150.03 mil²	109.51 mil (2.782 mm)
5 A	10 °C	1 oz	Internal	390.29 mil²	284.89 mil (7.236 mm)
10 A	20 °C	2 oz	External	256.27 mil²	93.53 mil (2.376 mm)

k = 0.048            # external; use 0.024 for internal
area = (I / (k * rise**0.44)) ** (1 / 0.725)   # mil^2
width_mil = area / (oz * 1.37)
print(area, width_mil, width_mil * 0.0254)       # last value in mm

2. Impedance models

Single-ended microstrip uses a closed-form approximation of the Hammerstad–Jensen type with a finite-thickness correction. Single-ended symmetric stripline uses the IPC-2141-style approximation Z0 = 60/√εr · ln[4b / (0.67π(0.8w + t))], where b is the plane-to-plane spacing, w the width and t the copper thickness.

The stripline expression is only meaningful for narrow traces. The calculator returns a number only when w/(b−t) < 0.35 and t/b < 0.25; otherwise it says why and shows no value. Closed-form results of this kind are estimates: real boards vary with etch profile, resin content, solder mask and glass weave. Ask your fabricator for their controlled-impedance stackup and tolerance, and treat the calculator as a starting point.

Design mode solves for the width that gives your target impedance by numerical search over the same formula. If no width in the accepted range reaches the target, the page says the target is out of range for that stackup. That does not mean the target is physically impossible; a different dielectric height or plane spacing can make it reachable.

3. What is switched off, and why

Clearance and creepage distances. The earlier implementation used simplified voltage buckets and fixed material multipliers that we could not tie to the published tables of the standard, and its default material group contradicted its own FAQ. Safety spacing depends on working voltage, overvoltage category, pollution degree, material group and altitude, and must be taken from the applicable standard (for example IEC 60664-1) or your certification body. No numeric output is shown.
Differential impedance. Two public approximations disagreed by about 3.6–4.1% on the same geometry, and there is no standard text or converged field solver in the pipeline to decide between them. Use your fabricator's field-solver result for coupled pairs.
Embedded microstrip. The earlier correction moved the impedance in the wrong direction relative to its own description and had no burial-depth input. Switched off until it can be verified.
Interface pages (USB, HDMI, PCIe, DDR, Ethernet, LVDS). These pages state nominal impedance targets and data rates only. Tolerance, skew and loss budgets are defined in the current interface specifications and device datasheets and are intentionally not reproduced here.

4. Known limits

The IPC-2221 power law is an older, generally conservative chart-based relation. IPC-2152 is the later standard for current capacity and accounts for effects (nearby planes, board thickness, airflow) that this calculator does not model. The calculators do not implement IPC-2152.
Results assume a straight uniform trace in still air; hot spots at vias, pads and necks are not modelled.
Via current uses the same power law on the plated-barrel cross-section and ignores thermal coupling to planes.
Impedance results ignore frequency-dependent loss, surface roughness and glass-weave skew.
Outputs are engineering estimates for early sizing. Confirm against the applicable standard, your fabricator's capability and, for safety-relevant designs, a qualified reviewer.

5. How we check the calculators

Trace-width examples are recomputed independently from the formula above (the 84 pre-rendered trace-width pages were all rechecked this way on 2026-10-14 with zero mismatches).
A fixed set of edge-case inputs (zero, negative, non-numeric, out-of-range, unit switches) is run against the calculators; NaN, Infinity, negative or stale results must not be displayed.
These checks test arithmetic and input handling. They do not validate the underlying models against measurements.

6. Change log

2026-10-14Stripline impedance now returns a value only inside its stated validity domain (w/(b−t) < 0.35 and t/b < 0.25); outside it the page shows the reason instead of a number.
2026-10-14Design-mode results (solved width, via count) now drive the displayed result, chart and copied text together. Previously the solved value was shown but secondary results and the copy text still described the old input.
2026-10-14The current-capacity quick-reference table is generated from the IPC-2221 formula. Corrected examples: 5 A at 1 oz and 10 °C rise is 109.5 mil (was 50 mil); 10 A at 2 oz is 142.4 mil (was 75 mil).
2026-10-14Clearance/creepage, differential-impedance and embedded-microstrip outputs were switched off because they could not be verified (see below). Unsourced tolerance, skew and length figures were removed from the interface pages.

Who maintains this site

This site is maintained by Jack Shi, Founder & CEO of NexaPioneer LLC (Boulder, CO, US), who is responsible for its content and for handling reports of errors. View Jack Shi on LinkedIn. This is an operating role: it is not an electromagnetic-simulation or product-safety qualification, and the calculators are design aids, not certified results.

Report a wrong number or unsupported claim through the contact page.

7. Corrections

If you find a wrong number, an unsupported claim or a broken calculation, send the page address, the inputs and the result you expected through the contact page. Confirmed errors are fixed and recorded in the change log above with the date of the fix.