What is a king stud vs. a jack stud?

King studs run full height alongside the opening, nailed to the header. Jack (trimmer) studs are shorter — they bear on the bottom plate and support the underside of the header. Together they carry the load around the opening.

Yes — cripples maintain stud spacing for sheathing and drywall nailing. Cripples above the header run between header top and top plate. For windows, sill cripples run from the bottom plate to the rough sill.

How big should the header be?

Per IRC R602.7, short spans (≤ 3.5 ft) use 2 × 2×6; up to 5 ft use 2 × 2×8; up to 6.5 ft use 2 × 2×10; longer spans need 2 × 2×12 or engineered LVL. Increase one size for two-story loads.

What is a "rough opening"?

The framed hole into which the door or window unit is installed, before trim. Manufacturers publish a rough opening size that is slightly larger than the unit to allow for shimming and squaring.

Does this work for window framing too?

Yes. Choose "Window" from the dropdown and the calculator adds sill plate and sill cripples to the lumber list.

Is this calculator free?

Yes — free, no signup, runs in your browser.

Door & Window Framing Calculator

Header size, king and jack studs, and cripples for any door or window rough opening.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this door & window framing calculator

Toggle inches or centimetres.
Pick the opening type (door or window) and the wall stud size (2×4 or 2×6).
Enter the rough opening width and height.
Set the wall height (96″ standard) and stud spacing (16″ or 24″ on-center).
Press Calculate to see header size, stud counts, cripples, and total framing lumber.

About this door & window framing calculator

The door & window framing calculator returns the lumber list for a framed rough opening: header size, king stud count, jack (trimmer) stud count, header cripples (the short studs between the top of the header and the top plate), sill cripples (between the bottom plate and the rough sill, for windows), and total linear feet of 2× framing. The header recommendation follows the IRC R602.7 table for one-story load conditions: short spans get 2 × 2×6, longer spans get 2 × 2×8, 2 × 2×10, or 2 × 2×12, each sandwiched with 1/2″ plywood to fill a 2×4 wall.

Worked example: a 36-inch-wide × 80-inch-tall door rough opening in a 2×4 wall, 96-inch ceiling, studs 16″ on-center. Header span ≤ 3.5 ft, so the recommendation is 2 × 2×6 with a plywood sandwich. King studs: 2. Jack studs: 2 (one each side, supporting the header). Cripples above the header: floor(36 / 16) = 2. Sill cripples: 0 (doors do not have a sill). Total framing lumber comes out to ~38 linear feet of 2× stock — enough for one 8-ft 2×4 plus a few shorter pieces from your offcuts.

Headers carry the load from above (joists, second story, or roof). The 2× sizes in the calculator assume a typical one-story load case. For multi-story loads, snow loads, or LVL/microlam headers, consult your local code and an engineer. Always crown rim joists and headers (bow up), and use proper hangers when you cannot bear directly on the jack studs.

FAQ

What is a king stud vs. a jack stud?: King studs run full height alongside the opening, nailed to the header. Jack (trimmer) studs are shorter — they bear on the bottom plate and support the underside of the header. Together they carry the load around the opening.
Do I need cripples?: Yes — cripples maintain stud spacing for sheathing and drywall nailing. Cripples above the header run between header top and top plate. For windows, sill cripples run from the bottom plate to the rough sill.
How big should the header be?: Per IRC R602.7, short spans (≤ 3.5 ft) use 2 × 2×6; up to 5 ft use 2 × 2×8; up to 6.5 ft use 2 × 2×10; longer spans need 2 × 2×12 or engineered LVL. Increase one size for two-story loads.
What is a "rough opening"?: The framed hole into which the door or window unit is installed, before trim. Manufacturers publish a rough opening size that is slightly larger than the unit to allow for shimming and squaring.
Does this work for window framing too?: Yes. Choose "Window" from the dropdown and the calculator adds sill plate and sill cripples to the lumber list.
Is this calculator free?: Yes — free, no signup, runs in your browser.