PCB conductor spacing method
PCB conductor spacing is selected from the voltage band and construction category. IPC voltage is DC or AC peak, so RMS AC input is converted before the lookup.
Vpeak = √2 × VrmsVlookup = VDC or Vpeakd = dtable for Vlookup ≤ 500 Vd = d500 + k × (Vlookup − 500) for Vlookup > 500 Vddesign = d × (1 + margin)where:
- Vpeak
- Peak value of an AC voltage difference[V]
- Vrms
- RMS value of the AC voltage difference[V]
- dtable
- Legacy table spacing for the selected voltage band and conductor category[mm]
- d500
- Spacing at the 301–500 V band[mm]
- k
- Additional spacing per volt above 500 V[mm/V]
- ddesign
- Spacing after the user-entered design margin[mm]
The lookup is a PCB layout reference based on publicly verifiable IPC-2221B values. Verify IPC-2221C and the applicable product-safety standard before design release.
How to use the PCB conductor spacing calculator
Choose whether to calculate minimum spacing from voltage or reverse an available edge-to-edge spacing into a reference voltage. Select the conductor environment carefully because an internal trace, an exposed external trace, a polymer-coated conductor, and a component lead use different lookup columns.
- Choose voltage-to-spacing or spacing-to-voltage mode.
- Enter DC, AC peak, or AC RMS voltage between adjacent conductors.
- Select the PCB or assembly conductor environment.
- Enter a fabrication and design margin.
- Review both millimetres and mils, then verify the current IPC edition and applicable product standard.
IPC PCB conductor categories
The construction category is part of the calculation, not a cosmetic label. Coated categories should only be used when the material and completed process meet the required construction definition.
| Category | Conductor condition | Typical interpretation |
|---|---|---|
| B1 | Internal conductors | Copper features separated within the PCB dielectric |
| B2 | External, uncoated, up to 3050 m | Exposed outer-layer conductors at normal and moderate altitude |
| B3 | External, uncoated, above 3050 m | Exposed outer-layer conductors at higher altitude |
| B4 | Permanent polymer coating | External PCB conductor with qualifying permanent polymer coating |
| A5 | Conformal-coated assembly | External conductor on the completed coated assembly |
| A6 | Component lead, uncoated | Exposed component lead or termination |
| A7 | Component lead, conformal coated | Coated component lead or termination |
Voltage basis: DC, AC peak, and AC RMS
The legacy IPC spacing table is indexed by DC voltage or AC peak voltage between conductors. When only a sinusoidal AC RMS value is known, the calculator uses Vpeak = √2 × Vrms. For example, 230 V RMS corresponds to approximately 325 V peak and therefore falls in the 301–500 V lookup band.
230 V AC RMS → approximately 325 V peak
400 V AC RMS → approximately 566 V peak
Use the maximum repetitive or applicable transient voltage required by the governing design method
Spacing above 500 volts
For voltage above 500 V, the legacy method adds a category-specific distance for every volt above 500 V. The calculator shows the table value before margin and the final design spacing separately so the source of the result remains visible.
| Category | Spacing at 500 V | Additional spacing above 500 V |
|---|---|---|
| B1 | 0.25 mm | 0.0025 mm/V |
| B2 | 2.50 mm | 0.0050 mm/V |
| B3 | 12.50 mm | 0.0250 mm/V |
| B4 | 0.80 mm | 0.00305 mm/V |
| A5 | 0.80 mm | 0.00305 mm/V |
| A6 | 1.50 mm | 0.00305 mm/V |
| A7 | 0.80 mm | 0.00305 mm/V |
PCB spacing versus clearance and creepage
PCB conductor spacing is a layout and manufacturability reference. Safety clearance is the shortest path through air, while creepage is the shortest path along an insulating surface. Equipment standards may also require pollution degree, material group, overvoltage category, altitude correction, reinforced insulation, slots, barriers, or dielectric testing.
PCB layout and manufacturing checks
The number produced by a spacing calculator is not automatically the CAD rule to release. Add the board fabricator's conductor-position and etching tolerances, then inspect pads, vias, component leads, test points, board edges, slots, mounting hardware, and coating keep-out areas.
- Measure spacing between conductor edges, not centre lines.
- Use net classes and design-rule checks for every relevant voltage domain.
- Do not assume ordinary solder mask is certified safety insulation.
- Review humidity, contamination, condensation, altitude, and coating process capability.
- Apply the product-specific IEC, UL, or other safety standard when isolation protects users or accessible circuits.
Assumptions
- Voltage is the DC value or AC peak difference between adjacent conductors
- Spacing is measured edge to edge
- Lookup values reproduce the publicly verifiable IPC-2221B Table 6-1 conductor categories
- The optional margin is applied after the table lookup
Important Warnings
- IPC-2221C is the current edition and must be checked for final design; this calculator transparently identifies its legacy-table data basis.
- IPC conductor spacing is not a substitute for clearance, creepage, dielectric withstand, or reinforced-insulation requirements in the applicable IEC, UL, equipment, or product standard.
- Solder mask and conformal coating are different construction categories; coating effectiveness depends on material, process, coverage, qualification, contamination, humidity, and service life.