Creepage and clearance calculator
Required spacing to IPC-2221B and IEC 60664-1 at once — because where they disagree is the number that matters.
Governing requirement
—mm
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The two distances
Clearance is the shortest path through air. It fails by the air breaking down — a spark. What governs it is peak voltage, air density and electrode geometry.
Creepage is the shortest path along the insulating surface. It fails by tracking: contamination and moisture form a conductive film, current flows, local heating carbonises the surface, and the carbon path grows until it bridges. That is a slow, cumulative failure, and it is why creepage depends on how dirty the environment is and how well the material resists carbonising.
IPC-2221B
A lookup by voltage band and conductor location, from Table 6-1. Above 500 V it becomes a per-volt increment. It is a fabrication-oriented table: it asks whether the board works, not whether a person is safe.
IEC 60664-1
Creepage is a function of working voltage, pollution degree and material group, interpolated logarithmically between the tabulated points. Clearance additionally depends on impulse withstand — which follows from the overvoltage category and the supply system, and is not something a calculator can infer for you. The clearance figure shown here is the basic requirement for the working voltage; if your product has a mains-derived impulse rating, that governs instead.
corrected clearance = clearance × altitude factor
≤2000 m ×1.00 4000 m ×1.29
3000 m ×1.14 5000 m ×1.48Slots and ribs
Creepage follows the surface, so lengthening the surface lengthens creepage. A milled slot between two conductors forces the path down one wall and up the other, adding roughly twice the slot depth. Clearance is unaffected — the air gap is still the straight line. This is why an isolation barrier on a well-designed board has a slot through it, and why grooves narrower than 1 mm are generally not counted by the standard.
Where this stops being sufficient
- Impulse withstand is not modeled. Mains-connected equipment is governed by overvoltage category and transient rating, which requires the full IEC analysis.
- Reinforced and double insulation have their own multipliers. This tool gives basic insulation.
- Coating only counts where it meets the standard's requirements for coverage and integrity. Conformal coating for environmental reasons does not automatically qualify.
- Component internals — an optocoupler's internal isolation comes from its own datasheet and safety approval, not from these tables.
- This is not a substitute for a safety assessment. On a certified product, a competent body signs this off.
Design guidance, not a manufacturing instruction. Verify every result against your fabricator's stack-up and the applicable standard before release. Closed-form models are approximations; the fab's field solver and process window are the authority.
Questions
What people ask about this
What is the difference between creepage and clearance?
Clearance is the shortest distance through air between two conductors. Creepage is the shortest path along the surface of the insulation. Creepage is almost always the larger requirement, because contamination and moisture build up on a surface and give current somewhere to track. A slot milled between two conductors lengthens creepage without changing clearance, which is exactly why you see them.
Why do IPC-2221 and IEC 60664-1 disagree?
They answer different questions. IPC-2221 is a bare-board electrical spacing table aimed at PCB fabrication, and it is concerned with the board surviving and functioning. IEC 60664-1 is an insulation coordination standard aimed at safety, and it accounts for pollution, material tracking resistance and impulse withstand. Where a product carries a safety requirement, IEC governs and IPC is not a defense. This tool shows both because seeing the gap between them is the point.
Which pollution degree applies to my product?
PD1 is a sealed or hermetic environment with no conductive contamination — rare, and you must be able to justify it. PD2 is normal indoor equipment where only non-conductive pollution occurs and occasional condensation is possible: this is the default for most electronics. PD3 is industrial or outdoor where conductive pollution or persistent condensation is expected. Choosing PD1 because the numbers are smaller is the most common way this analysis goes wrong.
What is a material group?
A classification by comparative tracking index — how well the insulating surface resists forming a conductive carbon path under contamination and voltage. Group I is the best at CTI ≥ 600; IIIb the worst at 100 to 175. Standard FR-4 is commonly Group IIIa or IIIb unless the laminate datasheet says otherwise, which is why assuming Group I is another common error.
Does coating let me reduce the spacing?
Under IPC-2221 a permanent polymer coating moves you from the uncoated external table to the coated one, which is a substantial reduction. Under IEC 60664-1 coating can qualify as insulation only if it meets specific requirements including complete coverage and no pinholes, and that has to be verified rather than assumed. Conformal coating applied for environmental protection does not automatically buy you a safety reduction.
Isolation barrier on a patient-connected or mains design?
Where the barrier sits decides the architecture, the board area and the connector choice. That is an early conversation, not a layout-stage one.