Creepage & Clearance Calculator
Reference estimate only. This implementation covers working voltages up to 1000 V, PD1–PD3 within the stored rows, and altitude from 0 to 6000 m. Clearance is an impulse-based estimate and does not evaluate every steady, recurring or temporary voltage stress. Certain PD3 creepage combinations are intentionally unavailable while current-edition table/applicability details are independently verified. It is not a complete implementation of IEC 60664-1 or a product-specific safety standard.
Method based on IEC 60664-1 Ed. 3.1 (2020 + A1:2025) · editorial check September 2026 · revision 1.2
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 this reference model arrives at each number
The tool implements the following simplified reference sequence:
- Clearance: the selected nominal supply-voltage band and overvoltage category select a rated impulse voltage from the stored Table F.1 reference data; that impulse maps to a clearance value in the stored Table F.2 data; pollution degree sets a floor; and above 2000 m the stored altitude factor is applied. Reinforced insulation uses the next stored impulse step. This is an impulse-based clearance estimate, not every clearance check that may apply to a product.
- 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).
- The stored PD2, IIIa rows give 2.0 mm at 200 V and 2.5 mm at 250 V. This implementation interpolates to 2.3 mm at 230 V. Confirm that this interpolation method applies to your equipment and edition.
- 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.
- The tool returns 3 mm clearance and 4.6 mm creepage for this stored-data example. These figures do not by themselves establish product compliance.
400 V working voltage, 600 V selected supply band, pollution degree 3
- Clearance: with 400 V working voltage, a selected nominal supply-voltage band up to 600 V and overvoltage category III, the stored model selects a 6 kV rated impulse, which maps to a 5.5 mm impulse-based clearance estimate.
- Creepage: 400 V at pollution degree 3 on material group IIIa uses the stored 6.3 mm reference value. The 600 V selection is the supply-band upper limit used by the model, not a claim that the actual supply is 600 V.
- Result under this bounded model: 5.5 mm impulse-based clearance and 6.3 mm creepage. Other voltage stresses and product-specific requirements still need separate assessment.
Overvoltage category - rated impulse voltage (Table F.1)
Overvoltage category is an installation/transient assumption, not a preference for a smaller clearance. Categories I to IV reflect different expected transient environments; familiar examples include protected secondary circuits, plug-connected equipment, fixed installations and the installation origin, but the applicable product standard and actual system arrangement still matter.
The full rated-impulse table (IEC 60664-1, Table F.1) is in the standard. This calculator uses the selected nominal supply-voltage band and overvoltage category to choose an impulse value from its stored reference model; it does not determine the category for the product.
Impulse-based clearance vs impulse voltage (Table F.2)
The stored reference map relates rated impulse voltage to an in-air clearance value for the model used here. Pollution degree 2 applies a 0.2 mm floor and degree 3 a 0.8 mm floor in this implementation. Other steady, recurring or temporary voltage stresses are not evaluated by this tool.
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)
This stored reference subset shows creepage for pollution degree 2 by material group. Pollution degree describes the insulation microenvironment, not a simple indoor/outdoor label. For an intermediate voltage this implementation interpolates between stored rows; verify the applicable conditions in the standard. Other pollution degrees and reinforced insulation use the separate rules implemented by the calculator.
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 an estimate from its stored subset; the worked examples show common cases.
Pollution degree and material group
Pollution degree describes the microenvironment at the insulation surface. Degree 1 is a protected microenvironment in which pollution has no influence. Degree 2 allows normally non-conductive pollution with only temporary conductivity caused by condensation. Degree 3 covers conductive pollution or dry non-conductive pollution that becomes conductive because condensation is expected. These are electrical microenvironment conditions, not automatic labels for office, indoor, outdoor or industrial locations. Coating or sealing does not automatically reduce the pollution degree; any reduction depends on the applicable protection method and requirements.
Material group ranks the insulator's resistance to tracking by its Comparative Tracking Index. Use the CTI documented for the actual insulating material and relevant formulation; do not assign a group merely because a material is marketed as FR-4 or belongs to another broad family. The calculator uses the CTI group as a creepage input, not as a material certification.
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 its stored clearance-correction factors above 2000 m and linearly interpolates between the stored altitude points. Those factors broadly match legacy public engineering references, but the amended current-edition altitude table has not been independently checked in full. The raw creepage table result is unchanged; the final reported creepage can still increase when the altitude-adjusted impulse-based clearance is larger.
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
Preliminary DC bus spacing up to this implementation’s 1000 V working-voltage limit, followed by the product-specific insulation checks.
Reinforced insulation barriers
Exploring a reinforced barrier under this tool’s simplified model. Medical and other product-specific requirements need separate assessment.
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 apply their own scope and insulation requirements and may use IEC 60664-1 insulation-coordination principles. The applicable product standard determines the final requirements. |
| IEC 60950-1 | Legacy AV/IT reference | Do not transfer old IEC 60950-1 spacing tables into a new product assessment without checking the applicable certification standard and edition. |
Related tools and standards
These estimates use a stored reference subset; 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) · UL Solutions — Comparative Tracking Index (CTI) / IEC 60112 overview. Verify against the current edition.