HomeCalculatorsElectricalPCB & Signal IntegrityPCB Trace Width Calculator (IPC-2221)
Electrical calculator

PCB Trace Width Calculator (IPC-2221)

Size PCB copper traces from current and temperature rise using the classic IPC-2221 I = k·ΔT^0.44·A^0.725 relation for external and internal layers. Runs locally in your browser.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance
Input interpretation
Enter values to calculate.
Result
—
Assurance
Engineering
Declared partition coverage
PASS · 4/4 declared partitions (width-external, width-internal, current, invalid-domain) · Matrix
Known limitations
  • IPC-2221 chart model — not IPC-2152; u_* deferred
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
PCB copper trace width or ampacity from IPC-2221-style I–A–ΔT relation; optional expanded uncertainty on the primary result.
Scope
Classic IPC-2221 closed form; not IPC-2152 charts.
Verification
Engine tested · Source checked · v1.1.1 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.1.1 · CVP protocol 1.0.0-proposed · Evidence 2026-09-11.schema-coverage-u
Verification revision
2026-09-11.schema-coverage-u · 6/6 property · digest 5252bebde7a8
Legacy regression
15/15 tests · Production surface contract 6/6
Reference
O1 model · O2 expected_values · O2 numerical_behavior
Interfaces
PASS · UI (SSR) / REST / MCP — ui-ssr is query-result HTML, not a live browser session.
Supplemental domain review
Internal · Pass · electrical-engineer
Named expert review
Not performed
CVP suite
3/3 golden · 5/5 CVP boundary · 4/4 invalid · 6/6 property · 1/1 cross-interface · 6/6 CVP contract · Manifest
Sources
  • IPC-2221 — Generic Standard on Printed Board Design — Conductor width and current capacity (external/internal k factors)
  • IPC-2152 — Standard for Determining Current-Carrying Capacity in Printed Board Design — Updated current-carrying methodology
Sources
Evidence
3 legacy golden · 6 legacy boundary · legacy regression suite · 3/3 oracle-backed golden · 4/4 invalid · Artifact integrity PASS · CalculatorX electrical review
This calculator CURRENT · Public schema 1.1.1 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓
Semantic contract
PASS
Full verification

Manifest identity, reference classes, interfaces, suite, and production records.

Formulas

Core equations used by this calculator.

Current vs areaI = k × ΔT^0.44 × A^0.725
Width from areaw = A / t (t ≈ 1.378 mil × oz)
iThis is the widely used IPC-2221 / design-handbook form for generic FR-4 copper. IPC-2152 charts may give different results for modern stacks; treat as a sizing estimate, not a thermal CFD.

How to use

1

Choose mode

Width from current (design) or current from width (check).

2

Enter ΔT and copper

Temperature rise above ambient (°C) and copper weight (oz/ft²).

3

Select layer

External (outer) uses k=0.048; internal uses k=0.024.

4

Optional uncertainties

Enter u(I) or u(width), u(ΔT), and/or u(oz) to show primary ± U (coverage factor 2 by default) via the Uncertainty Engine.

Example calculations

Common configurations with formula and result.

ϟ

10 A · 10 °C · 1 oz external

I=10 A · ΔT=10 °C · 1 oz · external

I = k·ΔT^0.44·A^0.725
w ≈ 283.2 mil (7.19 mm)
ϟ

Same · internal

I=10 A · ΔT=10 °C · 1 oz · internal

k=0.024
w ≈ 736.8 mil
ϟ

Ampacity check

Known width → solve I

mode=current
Round-trips to the design current
ϟ

With current & ΔT uncertainty

10 A · 10 °C · 1 oz external · u(I)=0.5 · u(ΔT)=1 · coverage=2

GUM sensitivity on width
w ≈ 283.2 ± 52.0 mil

PCB Trace Width Calculator (IPC-2221) specification

Version 1.1.1 · Engine tested · Supplemental domain review · Internal · 2026-08-10

Calculation status

Review policy · Evidence · Reviewed by CalculatorX electrical review (electrical-engineer)

Definition
IPC-2221-style trace sizing relates current I to cross-sectional area A (mil²) and allowable temperature rise ΔT via I = k · ΔT^0.44 · A^0.725, with k = 0.048 (external) or 0.024 (internal). Width follows from A and copper thickness (1 oz/ft² ≈ 1.378 mil).
What it calculates
PCB copper trace width or ampacity from IPC-2221-style I–A–ΔT relation; optional expanded uncertainty on the primary result.
Inputs
  • mode: width | current
  • I > 0 (A) when mode=width
  • width_mil > 0 when mode=current
  • dT > 0 (°C temperature rise)
  • copper_oz > 0 (oz/ft²), default 1
  • layer: external | internal
  • Optional u_I | u_width_mil, u_dT, u_copper_oz ≥ 0; optional uncertainty_k (default 2) or confidence
Outputs
  • width_mil, width_mm, area_mil2, I, dT, copper_oz, thickness_mil, k, layer, mode
  • uncertainty — optional; on width_mil (mode=width) or I (mode=current)
Formula
I = k·ΔT^0.44·A^0.725; w = A/(1.378·oz); k=0.048 external / 0.024 internal; optional U=k_cov·u_c
Assumptions
  • Classic IPC-2221 closed form; not IPC-2152 charts.
  • 1 oz/ft² ≡ 1.378 mil thickness.
  • Steady current; no via heating or nearby power planes.
  • When u_* are set, first-order GUM sensitivity with independent inputs (no ρ on this page).
Units
  • A, °C, oz/ft² → mil, mm, mil²
Boundary conditions
  • Missing I/width_mil/dT → MISSING_REQUIRED_INPUT
  • ≤ 0 → VALUE_MUST_BE_POSITIVE
  • Bad mode/layer → INVALID_MODE
  • Non-finite → INVALID_NUMBER
  • uncertainty_k without any u_* → INVALID_INPUT
Example
I=10 A, ΔT=10 °C, 1 oz external → width ≈ 283.2 mil
Validation cases

7 published on this page · 15/15 tests · Production surface contract 6/6 · View evidence

  • mode=width, I=10, dT=10, copper_oz=1, layer=external → width_mil≈283.232
  • mode=current round-trip from that width → I≈10
  • layer=internal same I/dT/oz → wider than external
  • u_I=0.5, u_dT=1 → width≈283.2 with uncertainty.U≈52 (coverage 2)
  • missing I in width mode → error MISSING_REQUIRED_INPUT
  • dT=0 → error VALUE_MUST_BE_POSITIVE
  • layer=mid → error INVALID_MODE
Sources
  • IPC-2221 — Generic Standard on Printed Board Design — Conductor width and current capacity (external/internal k factors)
    Supports: I = k·ΔT^0.44·A^0.725 with k=0.048 / 0.024
  • IPC-2152 — Standard for Determining Current-Carrying Capacity in Printed Board Design — Updated current-carrying methodology
    Supports: Context that IPC-2221 is a legacy closed-form estimate vs newer charts
Last reviewed
2026-08-10
Reviewed by
CalculatorX electrical review (electrical-engineer)
Calculation version
1.1.1

Background

Interpretation and common distinctions.

Size PCB copper traces from current and temperature rise with the classic IPC-2221 relation, or check ampacity from a known width. Optional standard uncertainties compose an expanded interval on the primary result via the Uncertainty Engine.

Default example: 10 A · 10 °C · 1 oz external → ≈ 283.2 mil (7.19 mm).

Supported and not supported

Supported

  • External / internal layer k factors (0.048 / 0.024)
  • Solve width from current or current from width
  • Copper weight → thickness via 1 oz ≈ 1.378 mil
  • Optional u_* on I/width, ΔT, and copper oz with coverage factor (default 2)
  • API result object via electrical.pcb.trace_width

Not supported

  • IPC-2152 chart interpolation / multi-layer stackups
  • Via current, plane spreading, or pulsed RMS derating
  • Controlled-impedance geometry (use a stackup tool)
  • Monte Carlo / correlation / νeff UI on this page (use Uncertainty Propagate directly)

Agent / API notes

Capability id: electrical.pcb.trace_width · tool id: pcb-trace-width · pin calculation_version: 1.1.1.

Stable error codes: MISSING_REQUIRED_INPUT, INVALID_NUMBER, VALUE_MUST_BE_POSITIVE, INVALID_MODE, INVALID_INPUT, VALUE_MUST_BE_NON_NEGATIVE.

SI/API fields: I (A), width_mil, dT (°C), copper_oz, layer, mode; optional u_*, uncertainty_k (coverage — not IPC k).

When any u_* is set, attaches uncertainty on width_mil (mode=width) or I (mode=current). Empty u_* preserves 1.0.0 nominal-only fields.

Other calculators in this family: Microstrip Impedance Calculator, PCB Differential Impedance Calculator, PCB Trace Thermal Calculator, Stripline Impedance Calculator, Via Current Capacity Calculator . Explore all PCB & Signal Integrity.

→ Microstrip Impedance Calculator Compute microstrip characteristic impedance Z0 from W/H/εr, or synthesize width for a target Z0 (zero-thickness IPC-2141 / Wadell–Hammerstad). Runs locally in your browser. › → PCB Differential Impedance Calculator Estimate edge-coupled microstrip differential impedance Zdiff from W, H, S, and εr. Hammerstad/Wadell Z0 plus IPC-2141A-style coupling. Runs locally in your browser. › → PCB Trace Thermal Calculator Estimate copper trace I²R power and temperature rise with a board thermal resistance. Runs locally in your browser. › → Stripline Impedance Calculator Estimate symmetric stripline characteristic impedance from W, b, and εr. Extends microstrip / Zdiff. Runs locally in your browser. › → Via Current Capacity Calculator Estimate PCB via ampacity from drill diameter, plating thickness, and temperature rise using the IPC-2221 I = k·ΔT^0.44·A^0.725 relation on the plating cross-section. ›
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Frequently asked questions

Key distinctions behind the calculation.

What is IPC-2221 trace width?

A handbook relation between current, temperature rise, and copper cross-section used to estimate minimum trace width on PCB outer or inner layers.

External vs internal?

External (outer) layers use k=0.048; internal layers use k=0.024 — internal traces need more width for the same current and ΔT.

Is 1 oz exactly 1.378 mil?

That conversion is the common calculator convention for 1 oz/ft² copper thickness. Fabrication plating and tolerances vary.

Does this replace IPC-2152?

No. IPC-2152 provides updated charts. This tool implements the classic closed-form IPC-2221-style estimate for quick sizing.

What if current or ΔT is missing?

The API rejects with MISSING_REQUIRED_INPUT or VALUE_MUST_BE_POSITIVE.

How do optional uncertainties work?

In mode=width, provide u_I, u_dT, and/or u_copper_oz to expand width_mil. In mode=current, provide u_width_mil, u_dT, and/or u_copper_oz to expand I. Coverage uses uncertainty_k (default 2) — not the IPC layer coefficient k. Composed via engineering.uncertainty.propagate.