Helical Pile Size Converter (in to mm)
Convert helical pile shaft and helix sizes between inches and millimetres, plus torque (ft-lb to N·m) and load (kips to kN), with a table of common sizes.
Convert
Exact conversion: 1 inch = 25.4 mm. Fractions like 2-7/8 work too.
Result
| Inches (decimal) | |
| Millimetres | |
| Centimetres | |
| Feet |
Torque: 1 ft-lb = 1.3558 N·m. Force: 1 kip = 4.4482 kN.
Helical pile sizes in inches and millimetres
Helical pile shafts in North America are sold by outside diameter in inches, often as fractions taken from standard steel pipe sizes. Canadian and international spec sheets list the same shafts in millimetres. The table converts the common sizes exactly (1 in. = 25.4 mm).
| Size | Inches | Millimetres |
|---|---|---|
| 1-1/2 in. square bar | 1.5 in. | 38.1 mm |
| 1-3/4 in. square bar | 1.75 in. | 44.5 mm |
| 2-3/8 in. round | 2.375 in. | 60.3 mm |
| 2-7/8 in. round | 2.875 in. | 73.0 mm |
| 3-1/2 in. round | 3.5 in. | 88.9 mm |
| 4-1/2 in. round | 4.5 in. | 114.3 mm |
| 5-1/2 in. round | 5.5 in. | 139.7 mm |
| 6-5/8 in. round | 6.625 in. | 168.3 mm |
| 8-5/8 in. round | 8.625 in. | 219.1 mm |
| 10-3/4 in. round | 10.75 in. | 273.1 mm |
| 12-3/4 in. round | 12.75 in. | 323.9 mm |
| 8 in. helix | 8 in. | 203.2 mm |
| 10 in. helix | 10 in. | 254.0 mm |
| 12 in. helix | 12 in. | 304.8 mm |
| 14 in. helix | 14 in. | 355.6 mm |
| 3/8 in. helix plate | 0.375 in. | 9.5 mm |
| 1/2 in. helix plate | 0.5 in. | 12.7 mm |
Wall thickness, helix count and rated torque matter as much as diameter. See the helical pile shaft sizes chart for which shafts suit decks, homes and commercial work.
Frequently asked questions
What is 2-7/8 inches in mm?
2-7/8 in. (2.875 in.) is 73.0 mm. It is the most common round shaft for residential and light commercial helical piles.
What is 1.875 inches in mm?
1.875 in. (1-7/8 in.) is 47.6 mm.
What is 12.75 inches in mm?
12.75 in. (12-3/4 in.) is 323.9 mm, a large-diameter shaft used for heavy commercial and industrial piles.
How do you convert ft-lb of torque to N·m?
Multiply ft-lb by 1.3558. A 7,000 ft-lb installation torque is about 9,491 N·m.
Sources
- NIST: SI unit conversion (Special Publication 811)
- CHANCE RS2875.203 data sheet
- ICC-ES AC358 (helix geometry)
Related guides and tools
Last reviewed October 2026 by the Helical Pile USA editorial team. Estimates are for planning only; a licensed engineer or installer sets the final design. Found an error? Tell us.
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