Window & Door Sizing Calculator

Instructions

Enter inches as decimals (e.g., 23.5). Choose your known dimension, then width and height. Adjust shim and sealant gaps to your spec. Select a profiled casing and optional sill nosing. Click “Calculate”.

Calculate using known

Width (in inches)*

Height (in inches)*

Shim Space (in inches)*

Sealant Gap (in inches)*

Profiled Casing

Sill Nosing

Results:

Options Selected
Calculate Using Known	—
Width (in inches)	—
Height (in inches)	—
Shim Space (in inches)	—
Sealant Gap (in inches)	—
Profiled Casing	—
Casing Size	—
Sill Nosing	—
Sill Nosing Size	—

Calculated Dimensions	Width	Height
Overall Unit Size	—	—
Rough Opening	—	—
Casing Dimensions	—	—
Masonry Opening	—	—

Key Features

✔ Clear, contractor-friendly UI with inputs for the known dimension, finished width/height, shim space, sealant gap, casing profile, and optional sill nosing.

✔ Start from what you know — calculate from Rough Opening, Overall Unit Size, Casing Dimensions, or Masonry Opening, and the tool derives the rest.

✔ Accurate add-ons using per-side casing adds (L/R/T/B) and sill nosing overrides for precise finished sizes.

✔ Instant, consistent results showing Overall Unit, Rough Opening, Casing, and Masonry dimensions side-by-side (Width & Height).

✔ Print-ready output with a single click to share specs with installers, suppliers, or clients.

How to Use It

Choose your starting point: Select Rough Opening, Overall Unit Size, Casing Dimensions, or Masonry Opening under “Calculate using known”.
Enter Width & Height: Type the values in inches (decimals like 23.5 are OK).
Set gaps: Enter Shim Space and Sealant Gap to match project requirements.
Select trim options: Pick a Profiled Casing and (if used) a Sill Nosing. The calculator applies the correct side/top/bottom adds.
Review results: Click Calculate. The right panel lists Overall Unit, Rough Opening, Casing, and Masonry dimensions (Width & Height).
Print or reset: Use Print to save/share the spec sheet, or Reset calculator to start fresh.

Size Windows & Doors with Confidence

This calculator removes guesswork by converting between unit size, rough opening, casing, and masonry dimensions with the correct allowances for shims, sealant, casing profiles, and sill nosing. Specify once, get every related dimension instantly, and send accurate cut sheets to the field or your supplier.

Window & Door Sizing Calculator