The familiar 2.84 × 1.42 m describes the free playing rectangle, not the cabinet or the room you need. Separate those three measurements before comparing a table, transferring a diagram or planning an installation.
Official carom geometry at a glance
Dimensions describe the free playing surface, not the outside furniture size.
Measure the playing area, then the cabinet
Article 11 of the cited UMB World Rules, the 1989 edition, specifies 2.84 × 1.42 m with a ±5 mm tolerance, a cushion nose 37 ±1 mm above the playing surface, and a floor-to-surround height of 75–80 cm. These are different measurement endpoints. Do not measure across the wooden outer edges and label that result the playing length.
For your survey, record the distance between opposite cushion noses along both axes and the manufacturer's overall cabinet dimensions separately. Also note the model and installation drawing. A seller's nominal size in feet is not a sufficient substitute. For comparison, the WPBSA 2024–25 rulebook gives the standard snooker playing area as 3569 × 1778 mm, with ±13 mm tolerance; it is not the same rectangle as a full-size carom table.
Diamond intervals are not the number of visible marks
UMB Article 11 sets the spacing at one eighth of the playing length. On the nominal full-size table, 2.84 ÷ 8 = 0.355 m, or 35.5 cm. That produces eight intervals along the long side and four along the short side: seven interior marks on a long rail and three on a short rail when corners are excluded.
Stand at one chosen corner, identify both endpoints and count spaces before assigning a system's numbers. The wooden diamond and the corresponding point on the cushion nose are different aiming references. A system may use unequal numbering or a projected sight line even though physical marks are equally spaced. Do not turn the count into a universal subtraction formula.
Calculate cue clearance on both sides
Here is a planning exercise, not a federation room standard. Choose cue length C and a separate backswing allowance B; assume an unobstructed rectangle and a cue-ball position at the playing edge. The provisional envelope is (2.84 + 2 × (C + B)) by (1.42 + 2 × (C + B)). All values in the table are metres; B = 0.15 is an illustrative choice, not a guaranteed comfortable stroke.
With a 1.45 m cue, C + B = 1.60 m, giving 6.04 × 4.62 m. Adding clearance only once underestimates the opposite side. Measure usable space at cue height, including radiators, columns and open doors. Mark the proposed playing rectangle on the floor and rehearse a level stroke along every side with the actual cue; never strike a ball on this mock-up.
| Cue C (m) | Allowance B (m) | Each side C + B (m) | Planning envelope (m) |
|---|---|---|---|
| 1.40 | 0.15 | 1.55 | 5.94 × 4.52 |
| 1.45 | 0.15 | 1.60 | 6.04 × 4.62 |
| 1.50 | 0.15 | 1.65 | 6.14 × 4.72 |
Why the room calculation is only the first check
The cabinet footprint, chairs, walking routes and space for other players may require more room. An off-centre table can fit one side and obstruct another. Check the widest delivery components, doors, stairs and turning space with the installer; floor loading and levelling are installation questions, not conclusions from the room formula. A shorter cue can help a particular obstruction but changes the equipment used for that shot.
The cited UMB provision calls for thermostatic heating for official tournament tables but does not prescribe a universal temperature in degrees. Obtain the table manufacturer's settings and electrical requirements. A playing-area measurement does not tell you heater consumption, floor strength or whether an existing table is approved for a particular event.
Transfer a practice diagram without promising the same rebound
Record a ball's location as fractions of measured length and width. In a purely geometric example, (0.25L, 0.50W) is (0.710, 0.710) m on a 2.84 × 1.42 m rectangle and (0.575, 0.575) m on an assumed 2.30 × 1.15 m rectangle. The second size is an example, not a universal club specification. Both mark the same relative location.
Keeping a 2:1 ratio preserves a scaled drawing's angles, not every real stroke. Ball size relative to the bed, spin, speed, cloth and cushion response need separate checks. Save the measured dimensions with your practice notes, test a simple reference route on the actual table, and adjust one input at a time. A diagram or simulator is not an installation survey or physical calibration.