Door Calculator
Estimate rough opening and door area
Width of the door slab
Height of the door slab
Thickness of the door jamb
Rough Opening Height
—
in
Door Area
—
sq ft
Rough Opening Width
—
in
Jamb Thickness
—
in
Disclaimer: Results are estimates based on standard formulas. Not a substitute for professional advice from a licensed contractor, engineer, or architect. Verify all calculations before making purchasing or construction decisions.
How to Use This Calculator
Framing a door opening? Getting the rough opening right is critical so the door fits, swings freely, and latches. Our calculator sizes the rough opening from your door slab dimensions.
- Measure the door slab width and height
- Enter the jamb thickness
- Run the calculator
- Frame the rough opening and allow for shimming and a level threshold
Expert Insights
Smart analysis for your Door project
Rough Opening Accuracy
Standard allowance is 2" wider and 2.5" taller than the slab. AI keeps shims, jamb legs, and a level threshold within tolerance.
Handing & Swing Clearance
Door swing must clear fixtures and furniture. AI reminds you to verify the swing arc against adjacent walls and cabinetry before finalizing size.
Accessibility Sizing
ADA-compliant doors need at least 32" of clear width. AI flags narrow doors and recommends 36" slabs for accessible entries.
Calculation Formula
Rough opening width = Door width + 2 x 2 in
Rough opening height = Door height + 2 in + 1.5 in
Door area = (Door width x Door height) / 144
Door Type Comparison
| Door Type | Typical Width | Height | Jamb Thickness | Best Use |
|---|---|---|---|---|
| Interior Slab | 28-36 in | 80 in | 4-9/16 in | Bedrooms, baths |
| Exterior Prehung | 32-36 in | 80 in | 4-9/16 / 6-9/16 in | Front, back entries |
| French Double | 60-72 in (pair) | 80 in | 5-1/4 in | Patio, wide openings |
| Pocket Door | 28-36 in | 80 in | N/A (in-wall) | Space-saving |
Authority References
Our calculations are based on guidelines and standards from these authoritative sources:
- Window & Door Manufacturers Association (WDMA) — Door Installation & Performance Standards. Learn more
- International Residential Code (IRC) — Section R311 — Means of Egress, Doors. Learn more
- Americans with Disabilities Act (ADA) — Door Clear Width Requirements. Learn more
Frequently Asked Questions
How do you calculate rough opening for a door?
Add 2 inches to the door width (1 inch per side for the frame and shims) and 2.5 inches to the height (2 inches for the header plus 1.5 inches for the threshold and sill).
What are standard interior door sizes?
Standard interior doors are 28, 30, 32, and 36 inches wide by 80 inches tall. A 30x80 inch door is the most common for bedrooms and bathrooms.
What is a door jamb thickness?
Standard interior door jamb thickness is 4-9/16 inches for 2x4 walls and 6-9/16 inches for 2x6 walls. Exterior doors often use 1-3/4 inch thick slabs.