Calculate the centerline arc length created by a reinforcing-bar bend. Change the bend angle or centerline radius and immediately see how the required curved length changes.
Enter bend geometry.
When a straight reinforcing bar is bent, the centerline follows an arc. The geometric arc length is θ × R, where θ is the angle in radians and R is the centerline radius. This tool calculates that curved centerline length and can convert an inside radius to a centerline radius by adding half the bar diameter.
Steel fabrication dimensions can be specified using different reference lines. Mixing inside radius, centerline radius and outside radius can create avoidable length errors. The calculator therefore makes the radius basis explicit.
For a 90° bend with an 80 mm centerline radius, the arc is approximately 125.66 mm. If 80 mm is instead an inside radius for a 16 mm bar, the centerline radius becomes 88 mm and the arc is approximately 138.23 mm.
| Angle | Arc fraction of a full circle |
|---|---|
| 45° | 1/8 |
| 90° | 1/4 |
| 135° | 3/8 |
| 180° | 1/2 |
| 270° | 3/4 |
No. Bend allowance is the curved length represented by the bend; bend deduction is an accounting adjustment used when deriving a flat or cut length from finished dimensions.
Only when the radius is specified relative to the inside of the bar. A directly supplied centerline radius already includes the diameter relationship.
Yes, provided the radius definition matches the actual geometry.