Calculate braid material length or finished length from braid factor, with in, ft, cm, and m units for quick length conversions anytime.
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Bolt Area Formula
The bolt area calculator uses different formulas depending on whether you are finding threaded tensile stress area or plain round shank area.
Unified inch thread tensile stress area
- At = tensile stress area of the threaded bolt, in²
- D = nominal major diameter, in
- n = threads per inch, TPI
Metric thread tensile stress area
- As = tensile stress area of the threaded bolt, mm²
- d = nominal major diameter, mm
- p = thread pitch, mm
Plain round shank area
- A = cross-sectional area of the round shank
- d = bolt or shank diameter
The standard size mode fills in the nominal diameter and thread value for common Unified and metric bolts. The inch thread mode uses the Unified tensile stress area formula with a custom diameter and TPI, or converts metric pitch to TPI first. The metric thread mode uses the metric tensile stress area formula with a custom diameter and pitch, or converts TPI to metric pitch first. The round shank mode finds the full circular area of an unthreaded bolt shank, which is larger than the tensile stress area of a threaded section.
Common Bolt Tensile Stress Areas
These values are useful for checking a result from a standard bolt size. Threaded tensile stress area is smaller than the plain shank area because the thread root reduces the effective cross-section.
| Unified bolt size | Major diameter | Thread | Tensile stress area |
|---|---|---|---|
| 1/4-20 UNC | 0.250 in | 20 TPI | 0.03182 in² |
| 3/8-16 UNC | 0.375 in | 16 TPI | 0.07749 in² |
| 1/2-13 UNC | 0.500 in | 13 TPI | 0.1419 in² |
| 1/2-20 UNF | 0.500 in | 20 TPI | 0.1600 in² |
| 3/4-10 UNC | 0.750 in | 10 TPI | 0.3346 in² |
| Metric bolt size | Major diameter | Pitch | Tensile stress area |
|---|---|---|---|
| M6 × 1.0 | 6 mm | 1.0 mm | 20.12 mm² |
| M8 × 1.25 | 8 mm | 1.25 mm | 36.61 mm² |
| M10 × 1.5 | 10 mm | 1.5 mm | 58.00 mm² |
| M12 × 1.75 | 12 mm | 1.75 mm | 84.27 mm² |
| M20 × 2.5 | 20 mm | 2.5 mm | 244.8 mm² |
Example Calculations
Example 1: 1/2-13 UNC tensile stress area
For a 1/2-13 UNC bolt, the nominal major diameter is 0.500 in and the thread count is 13 TPI.
The result is 0.1419 in², which is about 91.55 mm². The plain 0.500 in shank area is 0.1963 in², so the threaded tensile stress area is about 72.3% of the plain shank area.
Example 2: M10 × 1.5 tensile stress area
For an M10 × 1.5 bolt, the nominal major diameter is 10 mm and the pitch is 1.5 mm.
The result is 58.00 mm², which is about 0.08990 in². The plain 10 mm shank area is 78.54 mm².
FAQ
What is the difference between bolt area and tensile stress area?
Plain bolt area is the circular area based only on the outside diameter of the bolt or shank. Tensile stress area is the effective area of the threaded part of the bolt. For strength calculations involving a threaded fastener in tension, tensile stress area is usually the value you need because the thread root reduces the load-carrying cross-section.
Why is a fine-thread bolt area larger than a coarse-thread bolt area of the same diameter?
A fine thread has a smaller pitch, or more threads per inch. That means the thread depth is smaller, so the effective diameter used in the tensile stress area formula is larger. For example, a 1/2-20 UNF bolt has a larger tensile stress area than a 1/2-13 UNC bolt.
Which area should you use for bolt stress?
Use tensile stress area when calculating tensile stress in a threaded bolt section. Use plain round shank area only when the load is carried by an unthreaded shank section or when you specifically need the gross circular area based on diameter.
