PCB Clearance Calculator
Estimate recommended minimum air clearance between conductive features on a PCB based on voltage and environment.
Engineering estimate only. Always verify against IPC, IEC/UL, and product safety requirements for your market.
Designing safe PCBs is mostly about controlling electric fields where they can do damage. A reliable clearance rule helps prevent arcing, field breakdown, and latent reliability failures. This calculator gives you a fast starting point for voltage spacing decisions and helps you add practical design margin.
What this PCB clearance calculator does
This tool combines three things:
- Base spacing from common IPC-style voltage spacing bands.
- Altitude correction because thinner air reduces dielectric strength.
- Environment adjustments for pollution degree and conformal coating.
After the minimum is computed, the calculator applies your extra margin and compares it with your planned spacing in the layout.
Quick reference: example base spacing bands
These are common conservative bands used as a preliminary design reference for uncoated boards at normal altitude:
| Working Voltage | External Layer (mm) | Internal Layer (mm) |
|---|---|---|
| 0–15 V | 0.10 | 0.10 |
| 16–30 V | 0.10 | 0.10 |
| 31–50 V | 0.13 | 0.10 |
| 51–100 V | 0.25 | 0.13 |
| 101–150 V | 0.40 | 0.20 |
| 151–300 V | 0.60 | 0.25 |
| 301–500 V | 1.25 | 0.40 |
| 501–1000 V | 2.50 | 1.00 |
Clearance vs creepage (and why both matter)
Clearance
Clearance is the shortest distance through air between conductive parts. It protects mainly against arcing and flashover.
Creepage
Creepage is the shortest path along the board surface. It is strongly affected by contamination, moisture, and material group (CTI).
Many failures that seem like clearance problems are actually creepage failures on a dirty or humid surface. Good high-voltage design checks both.
How to use the calculator correctly
- Use the highest continuous working voltage, not the nominal marketing value.
- Select external for top/bottom exposed copper; internal for buried layers.
- Enter realistic altitude for worst-case operation or transport.
- Pick the right pollution degree: PD2 is common for indoor consumer/commercial gear.
- Add margin (10–30%) to absorb tolerance, contamination, and process drift.
Practical PCB layout tips for high-voltage spacing
- Route high-voltage nets with consistent spacing; avoid narrow choke points.
- Increase spacing near connectors and board edges where contamination is common.
- Use slots or cutouts to increase creepage without increasing board size.
- Keep solder mask assumptions realistic—mask is not always a safety insulation layer.
- Document spacing rules in your CAD constraints so DRC catches violations early.
FAQ
Is this calculator enough for certification?
No. It is a design aid. Certification requires product-specific standards and often test evidence.
Should I rely on conformal coating to shrink spacing?
Only if your compliance path allows it and your process quality is controlled. Coating defects can eliminate expected benefit.
What margin should I use?
For most products, 20% is a reasonable engineering starting point. Safety-critical and harsh-environment systems often use more.
Bottom line
A good PCB clearance rule is cheap insurance. Start with a conservative minimum, apply altitude and environment corrections, then add design margin. If your planned spacing clears the target with room to spare, your board is much more likely to pass review, testing, and long-term field operation.