Conduit Knockout and Punch Size Chart
Compare conduit trade sizes with published Greenlee round knockout punch diameters, including inch and metric references and product-family limits.
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Conduit-sized punch chart
A conduit-sized punch is named for a conduit trade size, but makes a larger opening. The following values are Greenlee published round-punch diameters. They are not conduit inside diameters, drill pilot-hole sizes, or a tolerance specification for every enclosure knockout.
| Conduit trade size | Published hole diameter (in.) | Published metric diameter (mm) |
|---|---|---|
| 1/2 | 0.885 | 22.5 |
| 3/4 | 1.115 | 28.3 |
| 1 | 1.362 | 34.6 |
| 1-1/4 | 1.701 | 43.2 |
| 1-1/2 | 1.951 | 49.6 |
| 2 | 2.416 | 61.4 |
| 2-1/2 | 2.914 | 74.0 |
| 3 | 3.539 | 89.9 |
| 3-1/2 | 4.044 | 102.7 |
| 4 | 4.544 | 115.4 |
Values are displayed as published and rounded in the manufacturer’s chart. Check the particular punch and connector drawing for the required opening and permitted tolerance.
Three different dimensions
| Dimension | Used for | Example of a wrong substitution |
|---|---|---|
| Conduit trade size | Naming a raceway/fitting size | Using 1/2 inch as the actual hole diameter for a 1/2 trade-size conduit punch. |
| Finished punch diameter | The opening made by the named punch | Treating this as the conduit bore for a fill calculation. |
| Draw-stud / pilot-hole requirement | Preparing the tool according to its instructions | Drilling the final opening when the tool requires a different pilot hole. |
| Connector entry specification | The opening and attachment required by the selected fitting | Assuming every threaded entry or proprietary connector accepts the same hole. |
For example, the 1-1/4 row identifies a 1.701-inch punch diameter in this family. That is not the OD or ID of 1-1/4 conduit and does not establish which threaded opening a separate product needs.
Confirm the tool and material
- Choose the exact punch/die and draw-stud system from the tool instructions; do not mix parts solely by nominal size.
- Check sheet material, thickness, tool capacity, and the selected product’s stainless-steel or other material limitations.
- Check the connector’s entry drawing and any enclosure modification restrictions before making an opening.
- Follow the tool’s operating and preparation instructions. This chart does not supply a drilling or punching procedure.
Use the conduit dimension tables for tube dimensions. Use the electrical box reference to distinguish factory knockouts and box features. This page provides a dimension lookup, not a conduit-fill or enclosure-rating result.