# Window Frame Length Calculator

> Work out the frame, mullion and transom profile lengths for a set of windows and how many stock bars to buy when the cuts are nested.

Category: Construction · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/window-frame-length-calculator

A rectangular frame needs two widths and two heights, plus a mullion or transom for each division. The calculator adds them up and nests the cuts into stock bars.

Also called: Window profile calculator.

## Inputs
- Frame width (outside) (unit mm; default 1200)
- Frame height (outside) (unit mm; default 1500)
- Profile face width (unit mm; default 60)
- Vertical mullions per window (default 1)
- Horizontal transoms per window (default 0)
- Number of windows (default 4)
- Bar length (unit mm; default 6000)
- Waste allowance on length (unit %; default 10)

## Results
- Bars to buy
- Profile per window
- Net profile length
- Length with waste allowance
- Mullion cut length
- Transom cut length

## Formula

```
Per window = 2W + 2H + Mullions × (H − 2f) + Transoms × (W − 2f);  Bars by first-fit decreasing nesting of all cuts
```

Where:
- W, H: outside frame size (mitred corners)
- f: profile face width

## Worked example
1. Mullion = 1,500 − 2 × 60 = 1,380 mm.
2. Per window = 2 × 1,200 + 2 × 1,500 + 1,380 = 6,780 mm; × 4 = 27.12 m.
3. Nesting: 8 heights fill 2 bars, 4 mullions 1 bar, 8 widths 2 bars → 5 bars.

**Result:** Four 1,200 × 1,500 mm windows with one mullion each need 27.12 m of profile, cut from 5 bars of 6 m.

## What the result means

Profile systems often have separate frame, sash and bead profiles; run the calculator once for each profile type.

## Assumptions and limits
- Outer frame members are cut to the full outside size with mitred corners.
- Mullions and transoms span the full inside of the frame; saw kerf is ignored.
- Where mullions and transoms cross, one of them is shorter in practice; the result slightly overstates length.
- Sashes, beads and glazing are not included.

## Questions

### What is the difference between a mullion and a transom?

A mullion is a vertical division; a transom is a horizontal one.

### Why add a waste allowance on top of nesting?

For miscuts, damaged ends and trimming. The bar count already accounts for unusable offcuts.

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- [Door Frame Material Calculator](https://calculators.geekmidst.com/calculators/door-frame-material-calculator)
- [Wall Stud Quantity Calculator](https://calculators.geekmidst.com/calculators/wall-stud-quantity-calculator)
- [Length Converter](https://calculators.geekmidst.com/calculators/length-converter)

_Quantities are estimates. Confirm requirements with your engineer or supplier before ordering materials._

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/window-frame-length-calculator