How many main tees and cross tees does a drop ceiling need?

Lay the mains out first: one line every 4 ft (1200 mm) across the room, at right angles to the joists, after equal borders at each wall. Each line of mains is the room's length in main beams. Cross tees then go between the mains every 2 ft (600 mm) along them, one in every bay and a cut border tee from each wall, so each line of cross tees takes one more tee than there are mains. In Armstrong's own sample room, 9 by 10 ft 6 in (2.74 by 3.20 m) with 2 x 4 panels, that is two lines of mains and five lines of cross tees, 15 cross tees in all.

What changes for 2 x 2 panels?

One short cross tee, 2 ft (600 mm) long, goes down the middle of every 2 x 4 opening to split it in two, so the long cross tees and the mains stay the same and the short tees are added. Armstrong lets the first main sit at the border width from the wall or the border plus 24 in (600 mm), so with 2 x 2 panels the mains fall on every other 2 ft (600 mm) grid line; the page puts the first on the first line.

How are the border panels worked out?

Armstrong's worksheet: divide the room by the panel, take the remainder, add one panel to it, and halve the result; that is the border at each wall. In its sample room, 9 ft (2.74 m) across 4 ft (1.22 m) panels is two panels and 1 ft (0.30 m) over, so each border is 2 ft 6 in (0.76 m); 10 ft 6 in (3.20 m) across 2 ft (0.61 m) panels is five and 6 in (0.15 m) over, so 1 ft 3 in (0.38 m). The borders come out the same on both sides and as large as possible, which is what Armstrong asks for.

How many hanger wires does the grid need?

Armstrong puts the wire fasteners 4 ft (1.2 m) apart along each main beam line, so each line takes its length over 4 ft (1.2 m), rounded up, and the page adds the lines together. Light fittings need extra wires of their own, the splices between main beams need a wire close by, and a seismic area or the grid maker's own table can call for more; the existing hanger page works the count from the area instead.

Why does a metric grid give a slightly different answer from an imperial one?

Because the modules are not the same size. A metric grid is laid on a true 600 mm (23.62 in) module, and an imperial grid on 2 ft (609.6 mm), so the borders differ by a few centimetres (an inch or so) where both fit the same number of lines, and by up to half a panel, 300 mm (11.8 in), where the metric grid fits one more line. On the 5 by 4 m (16.4 by 13.1 ft) room the borders come to 500 and 400 mm (19.7 and 15.7 in) on the metric grid against 476 and 366 mm (18.7 and 14.4 in) on the 2 ft one. The stock follows the grid too: 3.6 m (11.8 ft) main tees and 3 m (9.8 ft) wall angle for the metric grid, 12 ft (3.66 m) lengths for the 2 ft one. Pick the grid you are actually buying; the page sets each out on its own module.

Renovation & Construction

Drop or Suspended Ceiling Grid Calculator — Main Tees, Cross Tees, Wall Angle and Hangers

The whole drop (suspended) ceiling grid for a room: main beams, cross tees, wall angle and hanger wires, set out with equal border panels at each wall.

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Every formula citedNamed published standards
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SettingsSettings for this calculationUS

Market

Imperial · sales tax

Room Length

The room's length, wall to wall, at ceiling height.

Measure at the height the ceiling will hang, wall face to wall face. Check both ends: a room that is not square needs its borders cut to a taper, which no count captures.

Tools needed: Tape measure

Room Width

The room's width, wall to wall, at right angles to the length.

The page works the grid on the length and width as a rectangle; an L-shaped room is run as two rectangles.

Tools needed: Tape measure

Panel Size

The panels the grid holds: 2 x 2 or 2 x 4 ft, or 600 x 600 or 1200 x 600 mm.

Both use the same main beams and long cross tees; 2 x 2 panels add a short cross tee down the middle of every 2 x 4 opening. A metric grid is a true 600 mm (23.6 in) module and an imperial one 2 ft (610 mm), so pick the grid you are buying: the two set a room out slightly differently.

Which Way the Main Beams Run

Main beams run at right angles to the joists they hang from, Armstrong says.

Find which way the joists or the structure above run and lay the mains across them, so each hanger wire lands on a joist. The choice changes which dimension is divided into 4 ft (1200 mm) bays and which into 2 ft (600 mm) ones, and so the counts and the borders.

Main Beam Length as Sold

The length one main beam comes in: 3.6 m (11.8 ft) for the metric Prelude main tee, 12 ft (3.66 m) for Armstrong's.

The metric grid opens on the 3.6 m (11.8 ft) Armstrong Prelude main tee a UK merchant sells for 600 mm panels; the 2 ft grid on Armstrong's 12 ft (3.66 m) Prelude main beam, which Kanopi also sells 6 ft (1.83 m) long. Enter the length on the box you are buying.

Wall Angle Length as Sold

The length one piece of wall angle (wall molding) comes in: 3 m (9.8 ft) for the metric Prelude, 12 ft (3.66 m) for Armstrong's.

Armstrong's Prelude wall angle is sold in 3 m (9.8 ft) lengths in the UK and its wall molding in 12 ft (3.66 m) lengths in North America. Enter the length of the angle you are buying.

Hanger Spacing Along Each Main

How far apart the hanger wires go along a main beam: 4 ft (1.2 m) in Armstrong's instructions.

Armstrong snaps the lines for the mains 4 ft (1.2 m) apart and puts the wire fasteners 4 ft (1.2 m) apart along them. Light fittings take their own extra wires, and a seismic area or the grid maker's own table can call for closer spacing; enter what applies.

Main beams to order

5 main beams

High confidence

The grid follows Armstrong's instructions: main beams on the long module, cross tees between them on the short one, borders of the remainder plus one panel shared equally between opposite walls, a 2 ft (600 mm) tee splitting each opening for 2 x 2 panels, and hangers at the spacing entered along every main. Main beam offcuts start the next rows, as Armstrong suggests; cross tees are counted one to each opening, border tees included.

Lines of main beams: 3 lines
Long cross tees, border tees included: 32 tees
Short cross tees, for 2 x 2 panels: 27 tees
Wall angle pieces: 5 pieces
Hanger wires: 15 wires
Border across the mains, at each wall: 1.5 ft
Border along the mains, at each end: 1.25 ft
Perimeter for the wall angle: 59 ft

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

Armstrong World Industries, How to Install Your Armstrong Suspended Ceiling (general installation instructions): main beams installed perpendicular to the joists on 4' centres; snap chalk lines for main beams 4' apart and screw in wire fasteners 4' apart; cross tees 2' apart for 2' x 4' panels; border panels the same size on opposite sides and as large as possible, found from the remainder plus one panel length divided by two (the sample 9' x 10' 6" room: 2' 6" and 1' 3" borders); for 2' x 2' panels the first main beam at the border panel size or the border panel + 24" from the wall; additional hanger wires may be needed for light fixtures
Kanopi by Armstrong, How to Install Drop Ceilings: main beams carry the load of the grid, typically 12' or 6'; cross tees attach perpendicular to the main beams to make the 24" x 24" or 24" x 48" openings; wall moldings finish the perimeter; hanger wires attach to the joists; the left-over ends of cut main beams start additional rows
Kanopi by Armstrong, ceiling grid range: 12' Wall Molding, Prelude 12' Heavy Duty Main Beam, Prelude 2' Cross Tee
Judge Ceilings, Armstrong Ceiling Grid (UK merchant listing): 3.6m Armstrong Prelude Main Tees; Armstrong Prelude 1200mm Cross Tee; Armstrong Prelude 600mm Cross Tee; Armstrong Prelude Wall Angle 3m

Inputs used

Room Length: 16.5 ft
Room Width: 13 ft
Panel Size: 2 x 2 ft
Which Way the Main Beams Run: Along the room's length
Main Beam Length as Sold: 12 ft
Wall Angle Length as Sold: 12 ft
Hanger Spacing Along Each Main: 4 ft

Intermediate steps

Lines of main beams: 3 lines
Long cross tees, border tees included: 32 tees
Short cross tees, for 2 x 2 panels: 27 tees
Wall angle pieces: 5 pieces
Hanger wires: 15 wires
Border across the mains, at each wall: 1.5 ft
Border along the mains, at each end: 1.25 ft
Perimeter for the wall angle: 59 ft

Final result5 main beams

Confidence note: The grid follows Armstrong's instructions: main beams on the long module, cross tees between them on the short one, borders of the remainder plus one panel shared equally between opposite walls, a 2 ft (600 mm) tee splitting each opening for 2 x 2 panels, and hangers at the spacing entered along every main. Main beam offcuts start the next rows, as Armstrong suggests; cross tees are counted one to each opening, border tees included.

What this calculation does not cover

This counts the components of a standard lay-in grid in a rectangular room, laid out as the maker's instructions describe. It is not a design: hanger spacing in seismic areas, bracing, the weight the grid may carry and the support of light fittings, which Armstrong says may need additional hanger wires, are the grid maker's and the building code's.
Every cross tee position takes a whole tee, so the cut border tees each count as one. A 4 ft (1200 mm) tee cut for a narrow border sometimes leaves an offcut long enough for the opposite wall, which this count does not assume.
The main beams are the length of all the main lines over the stock length, using offcuts to start further rows; where the offcuts are too short to reuse, each line takes its own pieces and the count rises. Splices between main beam pieces need a hanger close by, which the spacing here does not place.
Wall molding is the perimeter over its stock length, with no allowance for the cut at every corner or for a wall out of straight; columns, boxing-in and bulkheads add their own runs.
Panels are counted on the ceiling tile page, which also gives the centred borders both ways.

Estimated cost — your price

Price per main beam ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-10-05 · v1.0.0

Regulatory standards & verification citations4

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Hanging a Suspended Ceiling

How to calculate drop or suspended ceiling grid — main tees, cross tees, wall angle and hangers in 8 steps

Room LengthThe room's length, wall to wall, at ceiling height.
Room WidthThe room's width, wall to wall, at right angles to the length.
Panel SizeThe panels the grid holds: 2 x 2 or 2 x 4 ft, or 600 x 600 or 1200 x 600 mm.
Which Way the Main Beams RunMain beams run at right angles to the joists they hang from, Armstrong says.
Main Beam Length as SoldThe length one main beam comes in: 3.6 m (11.8 ft) for the metric Prelude main tee, 12 ft (3.66 m) for Armstrong's.
Wall Angle Length as SoldThe length one piece of wall angle (wall molding) comes in: 3 m (9.8 ft) for the metric Prelude, 12 ft (3.66 m) for Armstrong's.
Hanger Spacing Along Each MainHow far apart the hanger wires go along a main beam: 4 ft (1.2 m) in Armstrong's instructions.
Main beams to orderThe tool computes the main beams to order from those figures and shows the formula, its sources, and a confidence rating alongside it.

Main beams to order by room length

Page defaults, not your figures above.

Room Length	Main beams to order (main beams)
10 ft	3
15 ft	4
20 ft	6
25 ft	7
30 ft	8

Frequently asked questions

How many main tees and cross tees does a drop ceiling need?: Lay the mains out first: one line every 4 ft (1200 mm) across the room, at right angles to the joists, after equal borders at each wall. Each line of mains is the room's length in main beams. Cross tees then go between the mains every 2 ft (600 mm) along them, one in every bay and a cut border tee from each wall, so each line of cross tees takes one more tee than there are mains. In Armstrong's own sample room, 9 by 10 ft 6 in (2.74 by 3.20 m) with 2 x 4 panels, that is two lines of mains and five lines of cross tees, 15 cross tees in all.
What changes for 2 x 2 panels?: One short cross tee, 2 ft (600 mm) long, goes down the middle of every 2 x 4 opening to split it in two, so the long cross tees and the mains stay the same and the short tees are added. Armstrong lets the first main sit at the border width from the wall or the border plus 24 in (600 mm), so with 2 x 2 panels the mains fall on every other 2 ft (600 mm) grid line; the page puts the first on the first line.
How are the border panels worked out?: Armstrong's worksheet: divide the room by the panel, take the remainder, add one panel to it, and halve the result; that is the border at each wall. In its sample room, 9 ft (2.74 m) across 4 ft (1.22 m) panels is two panels and 1 ft (0.30 m) over, so each border is 2 ft 6 in (0.76 m); 10 ft 6 in (3.20 m) across 2 ft (0.61 m) panels is five and 6 in (0.15 m) over, so 1 ft 3 in (0.38 m). The borders come out the same on both sides and as large as possible, which is what Armstrong asks for.
How many hanger wires does the grid need?: Armstrong puts the wire fasteners 4 ft (1.2 m) apart along each main beam line, so each line takes its length over 4 ft (1.2 m), rounded up, and the page adds the lines together. Light fittings need extra wires of their own, the splices between main beams need a wire close by, and a seismic area or the grid maker's own table can call for more; the existing hanger page works the count from the area instead.
Why does a metric grid give a slightly different answer from an imperial one?: Because the modules are not the same size. A metric grid is laid on a true 600 mm (23.62 in) module, and an imperial grid on 2 ft (609.6 mm), so the borders differ by a few centimetres (an inch or so) where both fit the same number of lines, and by up to half a panel, 300 mm (11.8 in), where the metric grid fits one more line. On the 5 by 4 m (16.4 by 13.1 ft) room the borders come to 500 and 400 mm (19.7 and 15.7 in) on the metric grid against 476 and 366 mm (18.7 and 14.4 in) on the 2 ft one. The stock follows the grid too: 3.6 m (11.8 ft) main tees and 3 m (9.8 ft) wall angle for the metric grid, 12 ft (3.66 m) lengths for the 2 ft one. Pick the grid you are actually buying; the page sets each out on its own module.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.