Enter door size and options to compute rough framing fast today easily. Compare inches and millimeters, then download shareable reports instantly for your crew.
Choose how you measured the door, set clearances, then calculate the rough opening.
The calculator converts everything into inches internally, then applies these relationships:
A practical ±0.25 in tolerance band is shown to reflect typical shim adjustability.
| Door size (W×H) | Assumed inputs | Rough opening (W×H) | Notes |
|---|---|---|---|
| 30 in × 80 in | Slab, jamb 0.75 in, shims 0.5 in, head 0.5 in, bottom 0.5 in | 33.5 in × 81.75 in | Common interior setup for standard framing. |
| 36 in × 80 in | Slab, jamb 0.75 in, shims 0.5 in, head 0.5 in, bottom 0.75 in | 39.5 in × 82.0 in | Extra bottom clearance helps with thicker flooring. |
| 914 mm × 2032 mm | Prehung, shims 13 mm, head 13 mm, bottom 19 mm, threshold 6 mm | 965 mm × 2083 mm | Exterior-like allowances in metric workflow. |
A correct rough opening keeps the unit square, prevents rubbing, and protects finishes. A small allowance around the frame leaves room for shims and minor stud variation. This calculator turns measurements into repeatable numbers, so the same door package can be framed consistently across rooms.
Door width and height are the base dimensions. If you measured a slab, the tool estimates the prehung unit by adding jamb thickness. If you measured a prehung unit, it uses that size directly. Shim space, head clearance, bottom clearance, and threshold allowance define the installation gap. Enter values that match your hardware and finish schedule.
Many crews allow about 1/2 inch per side for shimming and plumbing, plus about 1/2 inch at the head for leveling. Bottom clearance often ranges from 1/2 to 3/4 inch depending on flooring buildup. Exterior assemblies may need more for seals, sweeps, and sill components.
Interior doors focus on alignment and smooth operation. Exterior doors add water control and air sealing. A larger bottom allowance can accommodate a sill pan, thicker thresholds, or a raised finish floor. The exterior auto-adjust option raises bottom and threshold values to practical minimums when needed.
Projects may mix inches and millimeters when suppliers differ. The calculator converts all inputs to one internal unit, then reports both systems for fast checking. For reference, 1/2 inch is about 12.7 mm, and 30 inches is about 762 mm. Dual reporting reduces transcription errors.
Studs can twist, plates can crown, and sheathing can pull a wall out of plane. That is why the results include a small tolerance band around the target opening. Treat it as a practical range: if you land near an edge, plan extra shimming or light planing before trim. Recheck plumb at hinge locations.
The header helper adds two stud thicknesses to the rough width to reflect king stud placement. Use it for takeoffs and cut lists. Always confirm structural requirements for load-bearing walls, but consistent header lengths improve ordering accuracy and reduce waste on larger scopes.
After calculating, export the CSV for job notes or a shared folder. Use the PDF for a print-friendly rough-in sheet. Keeping a record of target openings, especially where floor finishes vary by room, helps reduce callbacks and prevents binding after the final floor is installed. Save one report per door label.
It is the framed hole in the wall where the door unit installs. It includes clearance for shimming, plumbing, and minor framing variation beyond the unit’s outside dimensions.
If you have the prehung unit dimensions, use them. If you only know slab size, select slab mode and provide jamb thickness so the calculator can estimate the unit size.
A common starting point is about 1/2 inch per side. Tight framing can work, but extra space improves adjustability when studs are crowned or walls are slightly out of plumb.
Head clearance helps level the unit, and bottom clearance accounts for flooring buildup, door sweep clearance, and threshold components. These allowances reduce rubbing after finishes are installed.
It shows a small practical range around the target opening to reflect real framing conditions. If your opening is near the edge, plan for extra shimming, minor trimming, or corrective framing.
No. It is a planning helper for material lists based on stud placement. Always follow project drawings and local requirements for load-bearing walls, spans, and fastener schedules.
CSV is useful for estimating and sharing door schedules, while PDF provides a clean printout for rough-in crews. Consistent records reduce callbacks and help verify openings before trim work.
Measure twice, frame once, and hang doors confidently always.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.