creepage clearance calculator

Why creepage and clearance matter

If you design PCBs, power supplies, battery systems, EV hardware, or industrial controls, insulation spacing is not optional. Two conductors that are too close can arc through air or track across a contaminated surface, causing electric shock risk, product failure, or fire.

This creepage clearance calculator helps you quickly estimate minimum spacing during early design, before you lock a layout or submit for certification.

What is the difference?

Clearance distance

Clearance is the shortest distance through air between two conductive parts. It protects against flashover due to transients (for example lightning impulses or switching spikes).

Creepage distance

Creepage is the shortest path along an insulating surface between conductive parts. It protects against surface tracking, which gets worse with dust, humidity, contamination, and lower CTI materials.

Inputs used in this calculator

• Working Voltage: Normal continuous voltage across insulation.
• Overvoltage Category (OVC): Expected transient severity level.
• Pollution Degree (PD): Environmental contamination severity.
• Material Group: Surface tracking resistance via CTI classification.
• Insulation Type: Basic or reinforced insulation requirement.
• Altitude: Higher altitude reduces air dielectric strength, increasing required clearance.

How the estimate is generated

1) Impulse withstand estimate

The calculator first estimates a rated impulse voltage from your working voltage and overvoltage category. This is a practical lookup approximation for concept-stage design.

2) Clearance from impulse + altitude correction

It maps impulse voltage to a base air gap, then applies an altitude correction factor above sea-level conditions. Reinforced insulation is treated conservatively by scaling spacing.

3) Creepage from voltage, PD, and CTI group

Creepage is estimated from stepped tables based on common IEC-style values. Dirtier environments and weaker tracking resistance push creepage distance higher.

Quick design example

For a 230 V product in OVC II, PD2, Material Group IIIa, Basic insulation at 2000 m:

• Estimated impulse withstand is typically around 2.5 kV.
• Clearance often lands near the low-millimeter range after mapping.
• Creepage often becomes the dominant requirement in polluted environments.

In many practical layouts, creepage ends up larger than clearance—especially on low-CTI materials.

Common mistakes engineers make

• Using only clearance and forgetting creepage.
• Ignoring altitude for high-elevation deployment.
• Choosing CTI group incorrectly for PCB base material.
• Applying basic insulation values where reinforced is required.
• Forgetting coating effects are standard-dependent and not always a free pass.

Practical PCB and product tips

• Use slots/barriers to improve creepage on crowded boards.
• Keep high-voltage nets away from board edges and mounting hardware.
• Add spacing margin early; certification changes late in the cycle are expensive.
• Document assumptions (PD, CTI, OVC, altitude) in your design file and test plan.

Final note

This calculator is a fast screening tool to guide design decisions. Final safety spacing must be validated against the applicable product standard (for example IEC 62368-1, IEC 61010-1, IEC 60601-1, UL equivalents, and local regulations), including your end-use environment, insulation system, manufacturing tolerances, and certification body interpretation.