Door Rough Opening Calculator
Rough opening size and header length for any door.
Enter your values
Enter the door width in in.
Enter the door height in in.
Enter the shim allowance each side in in.
Enter the jamb thickness in in.
Enter the floor clearance in in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Rough opening width
- 34.5 in
- Rough opening height
- 82 in
- Header length
- 37.5 in (RO + two jack studs)
- King stud spacing
- 40.5 in
- Finished opening
- 32 x 80 in
Working
- 132 + 2 x (0.75 + 0.5) = 34.5 in wide
Quick answer
Rough opening = door width + 2 inches and door height + 2.5 inches for a pre-hung door, giving room for jambs and shims.
RO width = door width + 2 in; RO height = door height + 2.5 in
At a glance
| What it does | Rough opening size and header length for any door. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Door width, Door height, Shim allowance each side, Jamb thickness, Floor clearance |
| Main output | Rough opening width |
| Formula | RO width = door width + 2 in; RO height = door height + 2.5 in |
| Cost | Free — no sign-up, no download |
How to use the Door Rough Opening Calculator
- 1Measure the door slab, not the old opening.
- 2Keep the default 1/2 inch shim space each side unless your framing is unusually true.
- 3Size the header for the span and load above the opening.
Inputs explained
- Door width(in)
- Enter the door width in in.
- Door height(in)
- Enter the door height in in.
- Shim allowance each side(in)
- Enter the shim allowance each side in in.
- Jamb thickness(in)
- Enter the jamb thickness in in.
- Floor clearance(in)
- Enter the floor clearance in in.
Worked example
Using the values the calculator loads with:
Inputs
- Door width32 in
- Door height80 in
- Shim allowance each side0.5 in
- Jamb thickness0.75 in
- Floor clearance0.75 in
Results
- Rough opening width34.5 in
- Rough opening height82 in
- Header length37.5 in (RO + two jack studs)
- King stud spacing40.5 in
- Finished opening32 x 80 in
- 32 + 2 x (0.75 + 0.5) = 34.5 in wide
Frequently asked questions
What is the rough opening for a 32 inch door?
About 34 inches wide by 82.5 inches high for a standard pre-hung interior door.
Can the opening be too big?
Slightly oversized is fixable with extra shims, but more than an inch of slop makes the jamb hard to hold plumb and square.
What do I need to enter into the Door Rough Opening Calculator?
Just 5 values: door width, door height, shim allowance each side, jamb thickness, floor clearance. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Door Rough Opening Calculator work out the answer?
Rough opening = door width + 2 inches and door height + 2.5 inches for a pre-hung door, giving room for jambs and shims. It applies the formula RO width = door width + 2 in; RO height = door height + 2.5 in and shows the working so you can check each step by hand.
Is the Door Rough Opening Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.