Second fix
Lining outer size
- where
- outside width (mm)
- clear width (mm)
- jamb / head thickness (mm)
- outside height (mm)
- clear height (mm)
- rough opening width and height (mm)
- fitting gap at each side (mm)
- fitting gap above (mm)
Explain this equation
Gives the outside size of a three-sided door lining from the clear opening you want, and the rough opening needed to fit it.
W and H are the clear width and height inside the lining, in millimetres. t is the thickness of the jambs and head. Wo and Ho are the outside sizes of the lining. gs is the fitting gap at each side, and gh the gap above. Wr and Hr are the rough opening sizes.
The width has a jamb at each side, so it gains 2t. The height has only a head at the top, with no threshold, so it gains just t. The rough opening adds a fitting gap at both sides and one above, leaving room for packing.
An 838 × 1981 mm clear opening with 32 mm material is 902 × 2013 mm outside. With 10 mm fitting gaps the rough opening is 922 × 2023 mm.
Watch out: jamb lengths and joints at the head depend on how the lining is made. They are not inferred here.
Calculate the outside frame size and rough-opening allowance.
Enter your values to see the result.
Good to know
Three-sided lining, no threshold. Jamb length and head joint details are not inferred from outside dimensions.
Sources
- Geometry / arithmetic
This is a calculation aid, not a structural design or compliance certificate. Every default is an example, not a specification for your project.