4 windows, 3×4 ft, 10% waste
- Perimeter per window = 2 × (3 + 4) = 14 ft.
- Total LF before waste = 14 × 4 = 56 ft.
- Total LF with waste = 56 × 1.10 = 61.6 ft.
- 8 ft boards ≈ 61.6 ÷ 8 ≈ 7.7 → plan on at least 8 boards (or 9 for extra safety).
construction calculator
Window Trim Calculator
Estimate linear feet and 8 ft boards for trimming windows.
Results
- Total trim (lf)
- 61.60
- 8 ft boards (approx)
- 8.00
How to use this calculator
- Count how many windows you plan to trim with the same casing style and dimensions.
- Measure or confirm the finished width and height of a typical window casing in feet.
- Enter the window count, width, height, and a waste allowance percentage.
- Review the total trim linear feet including waste and the estimated 8‑ft board count.
- Round the board count up to the next whole board and add a little extra if you expect complex cuts or future repairs.
Inputs explained
- Window count
- The number of windows you plan to trim with the same casing dimensions. If you have multiple sizes, run the calculator separately for each group.
- Window width (ft)
- The finished casing width for a typical window, measured edge to edge of the trim. Convert inches to feet (for example, 3 ft 4 in ≈ 3.33 ft) for consistent calculations.
- Window height (ft)
- The finished casing height for a typical window, again measured edge to edge of the trim, including the head and sill/leg pieces.
- Waste allowance (%)
- The extra percentage of trim you want to add for miter cuts, bad boards, and offcuts. Common values range from 10–20%, with more reserved for complex or high‑end profiles.
How it works
We take your window width and height (finished casing dimensions) to compute the perimeter for one window as 2 × (width + height).
We multiply that perimeter by the number of windows to get total linear feet of trim before waste.
We apply your waste allowance percentage to cover miter cuts, defects, pattern matching, and offcuts.
Finally, we divide the waste‑adjusted linear feet by 8 to estimate how many 8‑ft boards you should buy, rounding up in practice.
Formula
Perimeter per window = 2 × (Width + Height)\nTotal LF before waste = Perimeter per window × Window count\nTotal LF with waste = Total LF before waste × (1 + Waste% ÷ 100)\n8 ft boards ≈ Total LF with waste ÷ 8
When to use it
- Estimating casing trim for a set of standard‑size windows before heading to the lumberyard.
- Planning material takeoffs for interior or exterior window casings on remodels or new builds.
- Avoiding shortfalls caused by underestimating linear footage and miter waste.
- Comparing different trim profiles or window sizes to see how they affect total footage and board counts.
Tips & cautions
- Round board counts up and keep an extra board or two on hand for mistakes, damage, or future repairs.
- Increase the waste percentage for highly detailed profiles, complex casing layouts, or when you know you’ll need to match grain or patterns.
- Include sill extensions, aprons, or non‑standard head details as separate line items if they add length beyond the simple perimeter.
- If your supplier stocks different board lengths (10‑ft, 12‑ft, etc.), adjust your board calculations by dividing total linear feet by those lengths instead of 8.
- Assumes all windows in the calculation share similar casing dimensions; mixed sizes and styles should be handled with separate runs or more detailed takeoffs.
- Does not include non‑casing materials like caulk, fasteners, shims, or paint/stain—those need to be estimated separately.
- Does not account for layout choices such as continuous runs of trim or shared pieces between openings; it treats each window independently.
Worked examples
6 windows, 2.5×5 ft, 12% waste
- Perimeter per window = 2 × (2.5 + 5) = 15 ft.
- Total LF before waste = 15 × 6 = 90 ft.
- Total LF with waste = 90 × 1.12 = 100.8 ft.
- 8 ft boards ≈ 100.8 ÷ 8 ≈ 12.6 → round up to 13 boards.
Deep dive
This window trim calculator estimates total casing linear feet and 8‑ft boards so you don’t under‑order trim for your project.
Enter window count, width, height, and a waste allowance to get a quick trim takeoff you can bring to the lumberyard.
Ideal for contractors and DIYers planning interior or exterior window casing jobs who want fast, conservative material estimates.
Related calculators
This window trim calculator provides approximate material estimates based on simple perimeter math and a user‑entered waste factor. It does not replace detailed takeoffs, code requirements, or manufacturer guidance. Always verify measurements on site and consult local codes and product instructions before ordering materials or starting construction.