About this calculator
This calculator estimates the plasterboard, CD/UD metal frame, and consumable quantities for a suspended ceiling hung from the slab above — as opposed to a partition, which stands between floor and ceiling. Choose the room shape (rectangle, one of four non-rectangular templates, or a freely sketched shape), the CD grid spacing, the hanger spacing, the board size, and whether insulation sits above the boards.
Formula
The room shape is entered through the shared roomShape field, the same mechanism as the
ceiling-tile and floor-tile calculators. The ceiling area — used for the board count,
screws, and joint compound — is always the true polygon area of the chosen shape, not a
bounding-box estimate.
The suspended frame is a two-layer CD grid: bearing runs are hung directly from the slab by hangers, and furring runs clip onto the bearing runs (via cross connectors), perpendicular to them, at the same on-center spacing — the boards fix to the furring runs. A UD wall angle carries the grid's outer edge around the room's true perimeter.
furring run count = floor(bounding-box height / CD spacing) + 1
furring run length = furring run count × bounding-box width
bearing run count = floor(bounding-box width / CD spacing) + 1
bearing run length = bearing run count × bounding-box height
stock pieces (either run) = ceil(run length / profile stock length)
hangers per bearing run = floor(bearing run length / hanger spacing) + 1
hangers total = bearing run count × hangers per bearing run
cross connectors = bearing run count × furring run count
splice connectors (either run) = run count × max(0, ceil(single run length / stock length) − 1)
wall angle length = room's true perimeter
wall angle stock pieces = ceil(wall angle length / profile stock length)
boards (excl. waste) = ceil(room area / (board width × board height)) × layers
boards (incl. waste) = boards (excl. waste) + ceil(boards (excl. waste) × waste% / 100)
screws = ceil(room area × layers × screws/m² / 1,000,000)
joint compound = room area × joint compound kg/m²
Ceiling grid spacing is tighter than a partition's own stud spacing (the CD profile spacing
here defaults to 400 mm, versus 600 mm for drywall-partition's own CW studs) because a
ceiling board carries its own weight in bending, spanning between supports, rather than
standing flat against a vertical stud — a real structural reason, but not a citable load
table, so meta.standards is deliberately left empty (see Assumptions below).
Worked example
Defaults: room shape — rectangle 4 × 3 m, CD spacing 400 mm, hanger spacing 900 mm, 3000 mm stock profile, board 1200 × 2000 mm, 1 layer, 17 screws/m², 1.5 kg/m² joint compound, 10% waste.
bounding box = 4000 × 3000 mm
furring run count = floor(3000/400) + 1 = 8 (each spans 4000 mm)
bearing run count = floor(4000/400) + 1 = 11 (each spans 3000 mm)
furring stock pieces = ceil(8 × 4000 / 3000) = 11
bearing stock pieces = ceil(11 × 3000 / 3000) = 11
hangers per bearing run = floor(3000/900) + 1 = 4
hangers total = 11 × 4 = 44
cross connectors = 11 × 8 = 88
splice connectors = 8 (furring) + 0 (bearing) = 8
wall angle length = 2 × (4000+3000) = 14,000 mm → 5 stock pieces
room area = 12 m²
boards (excl. waste) = ceil(12,000,000 / 2,400,000) = 5
boards (incl. waste) = 5 + ceil(5 × 10/100) = 6
screws = ceil(12,000,000 × 17 / 1,000,000) = 204
joint compound = 12,000,000 mm² × 1.5 kg/m² = 18 kg
For these inputs the calculator returns exactly this: 6 boards (incl. waste), 8 furring and 11 bearing runs (11 stock pieces each), 44 hangers, 88 cross connectors, 8 splice connectors, a 14 m wall angle (5 stock pieces), 204 screws, and 18 kg of joint compound.
FAQ
Why do bearing and furring runs use the same spacing? The calculator has a single CD spacing input, applied to both layers of the grid. Real installations often space the bearing (primary) runners further apart than the furring (secondary) runners — this calculator models one shared spacing for simplicity. If you want a coarser bearing grid, use the resulting bearing run count as a starting point and adjust by hand.
Why does the frame use the room's bounding box instead of its true shape? CD and UD channels run in straight lines and are cut to fit on site — for a non-rectangular room, laying the frame out over the bounding box (rather than stopping and restarting at every notch) is closer to how it's actually installed. Only the frame (runs, hangers, connectors) uses the bounding box; the board count, screws, and joint compound all use the room's true area, so they aren't overstated for a notched room. The drawing shows the true room outline, with the CD grid lines clipped to it so a notch reads as empty — but that clipping is visual only. The run counts, lengths, and stock-piece totals above still cover each run's full bounding-box span, since the physical channel still runs straight through and gets trimmed on site, not cut short at the notch's own edge.
What are cross connectors and splice connectors? A cross connector joins a furring run to a bearing run at each point they cross. A splice connector joins two lengths of the same run end-to-end, needed only when a single run is longer than one stock piece.
Do hangers attach to both bearing and furring runs? No — only the bearing runs are suspended directly from the slab. Furring runs clip onto the bearing runs via cross connectors, so their own length doesn't get a separate hanger count.
What determines the screw density and joint compound coverage? Both are values you enter, with sensible defaults — they depend on the specific board and compound product, so the calculator doesn't derive them from any standard.
Why is the default screw density higher than drywall-partition's own wall-mounted rate? A ceiling board is fixed against gravity along its whole span, not just held to a vertical stud — the default here (17/m²) is higher than drywall-partition's own wall default (12/m²) for that reason, though both remain user-adjustable estimates, not derived figures.
Assumptions and limits
No standard was found that fixes CD/UD spacing, hanger spacing, screw density, or joint
compound coverage for a suspended plasterboard ceiling as a universal figure — these are set
by each profile/board manufacturer's own system (ETA/technical approval), so meta.standards
is deliberately left empty, the same reasoning drywall-partition's own metal-frame partition
gives for its CW/UW studs.
The CD frame (bearing runs, furring runs, hangers, cross connectors, splice connectors) is laid out over the room's bounding box, not its true polygon outline — for a non-rectangular room this is a reasonable, but not exact, take-off (see the FAQ above). Board count, screws, and joint compound all use the true polygon area.
Both the bearing and furring layers of the CD grid share a single spacing input, rather than each having its own — a stated simplification, not a derived design choice.
Drop height (slab to finished ceiling) and board thickness are reported back in the build-up section but don't otherwise drive any formula here — hanger wire length isn't modelled, since it depends on the specific hanger/wire system in use, which this calculator doesn't ask about.
The drawing shows the room's true outline, with the CD grid clipped to it and the board grid kept only where a board's centre falls inside that outline — for a large room, the CD lines and board grid are also decimated so the SVG stays legible. Neither the clipping nor the decimation affects the quantity calculations themselves.