Plasterboard
Jointing tape and joint compound (taped and jointed finish)
- where
- joint length (m)
- boarded area (m²)
- board width (mm)
- boards butt end to end: 1 = yes, 0 = full-height boards
- board length (mm)
- internal angles to tape (m)
- joint tape length (m)
- waste allowance (%)
- whole bags of compound to buy
- compound coverage per bag, metres of joint (m)
Explain this equation
This estimates the length of joints on a plasterboard area, the tape to cover them, and bags of jointing compound for a taped and jointed (not skimmed) finish.
A divided by the board width in metres gives the length of long-edge joints; A divided by the board length gives the end joints, switched on or off by ej. Li adds the internal angles. Cj is the maker’s coverage in metres of joint per bag.
Boards laid side by side make one long-edge joint for every board width across the area, so joint length per square metre is about one over the board width. The 1000 converts millimetres to metres. Compound is then joint length divided by coverage, rounded up.
Sense check: 1200 mm boards give about 0.83 m of long-edge joint per m², plus about 0.42 m/m² if boards are butted end to end. A 30 m² room with 10 m of angles has about 47 m of joints, one bag of EasiFill 60.
Watch out: the estimate is slightly high for a single small wall, where the outer board edges are corners, not joints.
Estimates the length of joints and internal angles on a plasterboard area, the paper tape to cover them, and bags of jointing compound from the manufacturer’s per-metre coverage.
Enter your values to see the result.
Good to know
British Gypsum publish jointing compound coverage per bag as linear metres of joint: EasiFill 60 and 45 about 84 m, Joint Filler about 68 m, ProMix Lite and Ready Mix about 68 m, Joint Cement about 118 m. Long-edge joints are about the area divided by board width; end joints add about the area divided by board length. Tape goes on flat joints and internal angles; external angles take bead or LevelLine instead.
Common mistake
Forgetting the internal angles: in a small room they can add as much tape as the flat joints.
Limits
The A ÷ B estimate slightly overstates joints in a single small wall (the outer edges are angles, not joints). For a precise figure measure the joints from the board layout. Screw spotting and extra feathering coats are included in the per-metre coverage figure only as far as the manufacturer’s figure allows.
Sources
- British Gypsum, Gyproc Jointing Selector Guide (coverage per bag in linear metres of joint: EasiFill 60 84 m, Joint Filler 68 m, ProMix Lite 68 m)
- British Gypsum, White Book: Jointing (taped and jointed finish, joint tape, beads)
- British Gypsum, BS sub-clauses (screws at max. 300 mm centres on walls, 230 mm on ceilings; 10 mm from bound edges, 13 mm from cut edges; dabs ≥ 20% contact)
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the manufacturers’ system and product data, BS 8212, BS EN 13914 and Building Regulations. Coverage rates vary by product, background and thickness. Check prices, VAT and CIS rules with your own records and HMRC.