PCB conductor spacing calculator (IPC-2221)
Minimum spacing between conductors for a peak voltage, from IPC-2221B Table 6-1, for each layer, altitude and coating condition.
- Table row used
- 301 to 500 V
- Condition
- B2: external, uncoated, sea level to 3050 m
| Volts | B1 | B2 | B3 | B4 | A5 | A6 | A7 |
|---|---|---|---|---|---|---|---|
| 0 to 15 | 0.05 | 0.1 | 0.1 | 0.05 | 0.13 | 0.13 | 0.13 |
| 16 to 30 | 0.05 | 0.1 | 0.1 | 0.05 | 0.13 | 0.25 | 0.13 |
| 31 to 50 | 0.1 | 0.6 | 0.6 | 0.13 | 0.13 | 0.4 | 0.13 |
| 51 to 100 | 0.1 | 0.6 | 1.5 | 0.13 | 0.13 | 0.5 | 0.13 |
| 101 to 150 | 0.2 | 0.6 | 3.2 | 0.4 | 0.4 | 0.8 | 0.4 |
| 151 to 170 | 0.2 | 1.25 | 3.2 | 0.4 | 0.4 | 0.8 | 0.4 |
| 171 to 250 | 0.2 | 1.25 | 6.4 | 0.4 | 0.4 | 0.8 | 0.4 |
| 251 to 300 | 0.2 | 1.25 | 12.5 | 0.4 | 0.4 | 0.8 | 0.8 |
| 301 to 500 | 0.25 | 2.5 | 12.5 | 0.8 | 0.8 | 1.5 | 0.8 |
| Over 500, per V | +0.0025 | +0.005 | +0.025 | +0.00305 | +0.00305 | +0.00305 | +0.00305 |
How this is calculated
V ≤ 500: spacing = Table 6-1 value for the row containing V V > 500: spacing = (301 to 500 V value) + k · (V − 500) k = 0.0025 (B1), 0.005 (B2), 0.025 (B3), 0.00305 (B4, A5, A6, A7) mm/V
- Voltage
- DC or AC peak between the two conductors. Mains RMS times 1.414: 120 V is 170 V peak, 240 V is 340 V peak.
- Columns
- B1 internal; B2 external uncoated to 3050 m; B3 external uncoated above 3050 m; B4 external with permanent polymer coating; A5 external with conformal coating over the assembly; A6 uncoated component leads to 3050 m; A7 conformal coated component leads.
- Scope
- This is the IPC printed board design spacing. Products under a safety standard (IEC 62368-1, IEC 60664-1) must also meet the creepage and clearance in that standard, which depend on pollution degree, material group and insulation type, and are not reproduced here.
- Revision
- Values are from Revision B (2012), as reproduced by EMA and Altair. IPC-2221C (December 2023) supersedes it and revises the electrical clearance guidance; its Table 6-1 was not checked here, so confirm against the revision your drawing calls out.
- IPC-2221B, Generic Standard on Printed Board DesignRevision B, 2012, Table 6-1
- Table 6-1 reproduction, PCB clearance distance tableEMA Design Automation, accessed 13 October 2026
- Table 6-1 reproduction and the B1 600 V worked exampleAltair PollEx, IPC Material reference, accessed 13 October 2026
Questions
240 V RMS is 340 V peak, which falls in the 301 to 500 V row: 2.5 mm on an uncoated outer layer (B2), 0.8 mm under a permanent polymer coating (B4), 0.25 mm on an internal layer (B1). A mains product must also meet its safety standard, which usually asks for more.
Clearance is the shortest path through air, creepage the shortest path along the insulating surface. IPC-2221 Table 6-1 gives a single conductor spacing. Product safety standards such as IEC 62368-1 and IEC 60664-1 set the two separately by pollution degree and material group.
Take the 301 to 500 V value and add the per-volt figure for each volt over 500. For an internal layer at 600 V: 0.25 mm + 100 × 0.0025 mm = 0.50 mm. For an uncoated outer layer at 1000 V: 2.5 mm + 500 × 0.005 mm = 5.0 mm.
Air breaks down at a lower voltage as pressure falls. Above 3050 m, column B3 applies to uncoated outer conductors: at 51 to 100 V it asks for 1.5 mm against 0.6 mm at sea level, and 12.5 mm from 251 V. Coating removes the altitude dependence (B4, A5).