Creepage & Clearance Calculator
Method based on IEC 60664-1 Ed. 3.1 (2020 + A1:2025) · reviewed June 2026 · method rev 1.0
Creepage vs clearance
Two distances, two failure mechanisms
Clearance is the shortest distance through air between two conductive parts. It exists to stop the air itself breaking down and arcing when a brief high-voltage transient appears on the line. What matters for it is the peak of that transient - the rated impulse voltage - the pollution degree, and the air pressure, which is why altitude comes into it.
Creepage is the shortest path between the same two parts measured along the surface of the solid insulation. It exists to stop tracking - a conductive carbonised path that grows slowly across a contaminated surface under the steady working voltage. What matters for it is the long-term rms or dc working voltage, the pollution degree, and how well the material resists tracking, expressed as its material group. Because a surface path can never be shorter than the straight line through air, creepage is always at least the clearance.
How the standard arrives at each number
The tool follows the general-purpose route of IEC 60664-1 for basic and reinforced insulation:
- Clearance: the mains nominal voltage and overvoltage category give the rated impulse voltage from Table F.1; that impulse voltage gives a clearance from Table F.2; the pollution degree sets a minimum; and above 2000 m an altitude factor is applied. Reinforced insulation uses the next impulse step up.
- Creepage: the working voltage, pollution degree and material group give the distance directly from Table F.4. Reinforced insulation doubles it. The result is then held to be no smaller than the clearance.
Worked examples
230 V mains, basic insulation, pollution degree 2
- Clearance: 230 V mains sits in the up-to-300 V band; overvoltage category II gives a 2.5 kV rated impulse (Table F.1), which needs 1.5 mm of clearance through air (Table F.2).
- Creepage: 230 V working voltage at pollution degree 2 on material group IIIa (typical FR-4) falls between the 200 V (2.0 mm) and 250 V (2.5 mm) points of Table F.4, so it interpolates to 2.3 mm - IEC 60664-1 permits linear interpolation between the two nearest points.
- Creepage must be at least the clearance; 2.3 mm already exceeds 1.5 mm, so the result is 1.5 mm clearance and 2.3 mm creepage.
The same 230 V, but with reinforced insulation
- Reinforced insulation steps the rated impulse up one step in the series, from 2.5 kV to 4 kV, which raises the clearance to 3 mm (Table F.2).
- Creepage doubles for reinforced insulation, so the 2.3 mm basic figure becomes 4.6 mm.
- Result: 3 mm clearance and 4.6 mm creepage - roughly double the basic-insulation case, which is exactly what reinforced insulation is meant to provide.
400 V industrial supply, pollution degree 3
- Clearance: a 400 V system on a 600 V mains in overvoltage category III gives a 6 kV rated impulse (Table F.1), which needs 5.5 mm of clearance (Table F.2).
- Creepage: 400 V at pollution degree 3 - a dirtier, more conductive environment - on group IIIa needs 6.3 mm (Table F.4), more than the same voltage would in a clean PD2 setting.
- Result: 5.5 mm clearance and 6.3 mm creepage. Here the pollution degree, not the voltage, drives the larger surface distance.
Overvoltage category - rated impulse voltage (Table F.1)
Where the equipment sits relative to the mains fixes the transient it must survive. Category I is behind protective measures (a low-voltage secondary); II is plugged into an outlet; III is part of the fixed installation; IV is at the service entrance.
The full rated-impulse table (IEC 60664-1, Table F.1) is in the standard. The calculator above selects the right impulse voltage for your mains and overvoltage category; the worked examples below show the common results.
Clearance vs impulse voltage (Table F.2)
Minimum clearance in air for an inhomogeneous field, the conservative case for real edges and points. Pollution degree 2 holds this to at least 0.2 mm, and degree 3 to at least 0.8 mm.
The full impulse-to-clearance table (IEC 60664-1, Table F.2) is in the standard. The calculator applies it to your impulse voltage; see the worked examples for typical figures.
Creepage vs working voltage (Table F.4, pollution degree 2)
Minimum creepage for the most common case - normal indoor pollution degree 2 - by material group. For an intermediate working voltage the next-higher row applies. Degree 1 is shorter; degree 3 is longer; reinforced insulation doubles these.
The full creepage table (IEC 60664-1, Table F.4) spans every working-voltage row for each material group and pollution degree. The calculator returns the right value for your inputs; the worked examples show common cases.
Pollution degree and material group
Pollution degree is the environment the surface sees. Degree 1 is no pollution - a sealed component or a conformally coated board. Degree 2 is normal indoor air where only occasional condensation is briefly conductive - offices, labs, most consumer and server equipment. Degree 3 is conductive pollution or condensation that is expected to occur - industrial and unheated spaces. Coating a board or sealing an assembly is a legitimate way to drop a degree and shorten the required creepage.
Material group ranks the insulator's resistance to tracking by its Comparative Tracking Index. A higher CTI tracks less readily and allows a shorter path. Most FR-4 sits in group IIIa; high-CTI laminates reach group I and can meaningfully reduce creepage on a dense board.
Altitude correction (clearance only)
Air thins with altitude, so it breaks down at a lower voltage and the air gap has to grow. The calculator applies the IEC 60664-1 clearance correction above 2000 m - the factor climbs gradually, on the order of 1.1x near 3000 m and about 1.5x near 5000 m. Surface tracking is unaffected by air pressure, so creepage does not change.
Where engineers use this
Mains-powered equipment
Spacing primary-side conductors for 120 V or 230 V at the pollution degree the product will actually see inside its enclosure.
Solar and energy storage
High-voltage DC bus spacing - 1000 V and up - often in dustier, higher pollution-degree outdoor conditions.
Reinforced insulation barriers
Doubling distances across the boundary between mains and an operator-accessible or SELV side in instrumentation and medical gear.
Frequently asked questions
What is the difference between creepage and clearance?
Why is creepage always at least as large as clearance?
How does pollution degree change the result?
What is a material group and where do I find the CTI?
Why does altitude only affect clearance?
Does this replace the full standard?
How this relates to other standards
| Standard / tool | Relationship | What it means |
|---|---|---|
| IEC 62368-1 / IEC 61010-1 | Applied by | Product safety standards draw their clearance and creepage tables from IEC 60664-1; the product standard sets the final required number. |
| IEC 60950-1 | Replaced by | Withdrawn 20 December 2020; AV/IT spacing now lives in IEC 62368-1 sub-clauses 5.4.2/5.4.3, not the old 60950 tables. |
Related tools and standards
These are the general-purpose IEC 60664-1 tables for basic and reinforced insulation; the product standard that applies to your equipment (for example IEC 62368-1 or IEC 61010-1) sets the final required distance.
Sources: IEC 60664-1, Insulation coordination for equipment within low-voltage supply systems, Ed. 3.1 (2020 + Amendment 1:2025). Verify against the current edition.