Sheet Metal Calculator for Bend Allowance and Flat Length

This sheet metal hub calculates bend allowance for a flat blank. Enter thickness, inside radius, bend angle, and K-factor. It does not size press-brake tonnage.

Use inside flange lengths when you add bend allowance, or outside flange lengths when you subtract bend deduction. The K-factor is a starting value. Confirm it with a test coupon before a production blank. Cutting RPM stays on the speeds and feeds calculator.

What is a sheet metal calculator?

A sheet metal calculator on this site answers one forming question: how long the flat blank must be for a single bend. The formula is BA = (π/180) × angle × (R + K × T). Inside flanges add that allowance. Outside flanges subtract the bend deduction.

• Use it for one air-bend flat pattern in inches or millimetres.
• Do not use it to estimate press-brake tonnage or V-die opening.
• Do not treat the sample K-factor 0.44 as a measured coupon.

Core tools

Start here

Most visits need the flat length of one 90° bend. Open the bend allowance calculator, keep inside flanges selected when the legs stop at the bend, or switch to outside flanges when the drawing shows outside dimensions. After the blank is cut, use speeds and feeds only if the next operation is milling or drilling.

Open bend allowance calculator

Workflow

1. Add bend allowance to inside flanges on the bend allowance calculator.
2. Switch the same page when the drawing uses outside dimensions: outside flange flat length.
3. Check cutting RPM only after the blank exists, with the speeds and feeds calculator.

Use cases

• 16 gauge, 90° inside: 0.060 in, radius 0.060 in, K 0.44, legs 2 in and 1 in → bend allowance 0.1357 in and flat 3.1357 in. Calculate the inside flat.
• Same bend, outside dimensions: subtract bend deduction 0.1043 in from the 2 in and 1 in outside legs. Calculate the outside flat.
• 2 mm, 90° inside: radius 2 mm, K 0.40, legs 50 mm and 30 mm → flat 84.398 mm. Calculate the metric flat.

Which tool for which job

FAQ