What the Box Flat Pattern Calculator does
This tool turns a finished box size into the flat sheet you cut to make it. Enter the outside length, width and height of an open-top box, the material thickness, the inside bend radius and the K-factor, and it returns the developed flat blank size, the bend deduction per bend, the blank area and the weight. It is built for enclosure and machine builders who fold trays and covers on a press brake.
It uses the standard 90-degree bend-deduction formula, so the blank folds up to the exact outside dimensions you entered. The flat pattern is drawn live so you can see the base, the four walls and the corner notches.
How to use it
- Set the box length, width and height (outside dimensions, mm).
- Set the material thickness, inside bend radius and K-factor.
- Choose the material and the quantity.
- Read the flat blank size to cut, with the bend deduction, blank area and weight below.
Why use it here
It is free, instant and private, with no sign-up. It gives the blank size, bend deduction and weight together, which is exactly what you need to nest, cut and quote an enclosure body. The live unfold diagram makes it easy to check the base, walls and corner relief before you cut.
Tip: for a single bend rather than a whole box, use the bend allowance calculator; to size the press for the job, use the press brake tonnage calculator; and to nest the blank on a sheet, use the sheet yield calculator.
Frequently asked questions
- How is the flat blank size calculated?
- An open-top box is bent from one blank with four 90-degree bends: the base plus four walls. The developed length is L + 2H − 2·BD and the width is W + 2H − 2·BD, where BD is the 90-degree bend deduction, BD = 2(R+T) − (π/2)(R + K·T). The tool shows the blank, the bend deduction and the weight.
- What box type does it assume?
- An open-top tray: a base with four walls folded up, four bends, with corner relief notches. This is the typical body of an electrical enclosure or machine cover. Add a separate lid as its own part if you need one.
- Why subtract a bend deduction?
- When metal bends, the outside stretches and the inside compresses, so the flat length is shorter than the sum of the outside dimensions. The bend deduction removes that difference, once per bend, so your cut blank folds up to the exact outside box size.
- Does it give the blank weight?
- Yes. It multiplies the bounding blank area by the thickness and the material density, and by the quantity for a batch. The bounding blank is what you shear before notching the corners.
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Last updated: June 23, 2026