The Coffered Ceiling Calculator plans a coffered ceiling grid: it calculates the opening size of each coffer, the total length of beams, and the area of cladding (sheet material or boards) to wrap the beams.
Enter the room size, how many coffers you want each way, beam width and depth, and whether beams run along the walls. The coffers are spaced evenly so the grid looks balanced.
Coffered Ceiling Calculator
Coffer size, total beam length and sheet material for a coffered ceiling grid.
Formula
- Coffer opening (length): (L − (nL − 1 + 2p) × b) ÷ nL
- Coffer opening (width): (W − (nW − 1 + 2p) × b) ÷ nW
- Total beam length: (nW − 1) × L + (nL − 1) × W + p × 2(L + W)
- Cladding area: beam length × (b + 2d) − p × 2(L + W) × d
Where L, W = room length and width; nL, nW = coffers each way; b = beam width; d = beam depth; p = 1 with perimeter beams, 0 without.
How the Calculation Works
Step 1: Subtract the widths of all beams across each direction from the room size.
Step 2: Divide what’s left by the number of coffers to get each opening.
Step 3: Add up interior beams (running the full room length or width) and any perimeter beams.
Step 4: Cladding covers each beam’s bottom and two sides; beams against a wall need only one side.
Variables Explained
| Input | Meaning |
|---|---|
| Coffers along length / across width | Number of recessed panels each way |
| Beam width | Visible bottom face of each beam |
| Beam depth | How far the beam drops below the ceiling |
| Perimeter beams | Whether beams also run along the walls |
Example Calculation
Given: 20 × 12 ft room, 4 × 3 coffers, 6 × 6 in beams (0.5 ft), perimeter beams
Opening along length = (20 − 5 × 0.5) ÷ 4 = 4.375 ft (4 ft 4½ in)
Opening across width = (12 − 4 × 0.5) ÷ 3 ≈ 3.33 ft (3 ft 4 in)
Beam length = 2 × 20 + 3 × 12 + 2 × 32 = 140 ft
Cladding = 140 × (0.5 + 1.0) − 64 × 0.5 = 178 ft²
Shape Properties
- Square-looking coffers come from choosing coffer counts that make both openings similar.
- Deeper beams need a higher ceiling to avoid making the room feel low — check headroom with the Ceiling Height Calculator.
Material Estimation Notes
- Beam length is the run of beams; framing, blocking and trim (crown, panel molding) are extra.
- Buy cladding in sheet or board sizes and add waste for cuts and miters.
- Fixing beams to joists and any electrical work should follow local code.
Frequently Asked Questions
How do I calculate coffered ceiling spacing?
Subtract all beam widths from the room dimension, then divide by the number of coffers.
How many coffers should my ceiling have?
It is a design choice; try different counts until the openings look balanced for the room.
How much beam material do I need?
The total beam length above, plus the cladding area for the bottom and sides.
Do I need perimeter beams?
They frame the edges neatly; without them the outer coffers run to the walls.
Does this work in metric?
Yes — enter all dimensions in metres.