A canopy is the ceiling plate that hides the junction box and the hole the wiring passes through. It carries no weight: the box and its brace do. A US chandelier canopy is usually 5 in (127 mm) across, which leaves about 13 mm of cover on each side of a 4 in (102 mm) box.
What a canopy does, and what it does not do
A canopy is a pressed metal cup, open at the bottom, that sits against the ceiling and closes the point where a stem, chain or cable leaves the building. It does three jobs and only three. It covers the box and the plaster opening so the wiring is not visible. It makes the transition from a 10 mm stem or a 4 mm chain to a 127 mm ceiling read as deliberate rather than improvised. And it gives the installer a surface to tighten against, so the fixture hangs plumb. It does not carry load, it is not a fixing point, and it is not a structural bracket, even when it is 200 mm across and 1.5 mm thick. Load goes into the box, into the brace above the box, or into a beam. A canopy that is asked to do structural work deforms at the screw slots first, and the fixture drops by the depth of the deformation before anything else fails.
| What the canopy does | What actually does it |
|---|---|
| Covers the box and the plaster opening | Canopy diameter against opening size |
| Hides the stem, chain or cable entry | Canopy height and the collar at the top |
| Gives a plumb line to tighten against | Screw slots and the box thread |
| Carries the fixture | Ceiling box, brace or beam, never the canopy |
Canopy size against the ceiling box
The number that decides whether a canopy fits is the width of the box opening, not the diameter of the fixture. US ceiling boxes come in trade sizes that are named by their width: 3-1/2 in (89 mm) octagon, 4 in (102 mm) octagon, and 4-11/16 in (119 mm) square, with a 4 in box being the one in most residential ceilings. A 5 in (127 mm) canopy over a 4 in (102 mm) box leaves 12.7 mm of cover on each side, which is enough for a flat ceiling and not enough for a ceiling that is out of level by more than a few millimetres. The same canopy over a 4-11/16 in (119 mm) box leaves 4 mm per side, and a 4 mm reveal looks like a mistake at eye level. These box sizes are US trade sizes and a wiring convention, not a rule that sets canopy diameter; the pairing below is what installers expect, not a standard.
| Box trade size | Opening across | Canopy that covers it cleanly | Cover per side |
|---|---|---|---|
| 3-1/2 in octagon | 89 mm | 4 in (102 mm) or larger | 6.4 mm at 4 in |
| 4 in octagon | 102 mm | 5 in (127 mm) | 12.7 mm |
| 4-11/16 in square | 119 mm | 6 in (152 mm) | 16.7 mm |
| 4-11/16 in square, tight ceiling | 119 mm | 5 in (127 mm) | 4 mm, visibly tight |
When a canopy is too small
A canopy is too small in four situations, and each has a different remedy. The first is a box wider than the canopy, which happens when a 4-11/16 in (119 mm) box is paired with a 5 in (127 mm) canopy and the corners of the box show past the rim. The second is a plaster opening left by an earlier fixture, often 150 mm or wider where a ceiling fan or a recessed housing was removed, which no stock canopy covers. The third is a sloped ceiling, where a flat canopy touches on the low side and stands off on the high side. The fourth is a medallion or a textured ceiling that holds the rim 5 mm off the plaster, so the gap reads as a shadow line all round. Measure the opening, not the old canopy: a replacement that matches the old diameter can still be too small for the hole underneath it.
| Symptom | Cause | Remedy |
|---|---|---|
| Box corners visible past the rim | Canopy smaller than the box opening | 6 in (152 mm) canopy or a medallion |
| Dark ring between rim and plaster | Ceiling out of level, or texture holding the rim off | Medallion, or a canopy with a deeper skirt |
| One side touching, one side open | Flat canopy on a slope | Swivel canopy or a slope adapter |
| Hole wider than any stock canopy | Earlier fixture left a large opening | Patch the ceiling, then fit a 5 in canopy |
Slope: when a flat canopy leaves a gap
On a slope, the gap under a flat canopy is the diameter multiplied by the tangent of the angle: 127 mm across a 30 degree slope stands off about 73 mm on the high side, and the same canopy on a 45 degree slope stands off 127 mm, which is a visible opening rather than a shadow line. A swivel canopy solves this because the cup rotates on a ball or a yoke and stays flush while the stem follows the slope. A slope adapter does the same job with a wedge. Both are separate parts, and both must be ordered with the fixture rather than after it, because the thread and the collar diameter have to match. A canopy that is screwed down hard onto a slope instead of swivelling distorts the rim and, over a season, works the screws loose.
Load: what holds a chandelier up
The canopy is the last part in the load path and the weakest. A ceiling box is rated for the fixture it was installed for, and a box fixed to a joist with two screws is not the same anchor as a box on a braced bar between joists. Above about 20 kg (44 lb) the question stops being about the canopy and becomes about the brace, the joist and the fixing method, and the answer belongs to an electrician on site rather than to a supplier. The canopy only has to survive the torque of its own screws. This is also where listings go quiet: of 1,829 active listings in our own catalogue, 1 states a net or gross weight, so a buyer comparing a 40 kg body against a 12 kg ceiling box has nothing to compare.
What to measure before ordering a replacement
Four measurements decide a replacement canopy, and all four are taken with the fixture down. Measure the box opening across its widest point, corner to corner on a square box, and note whether it is 4 in (102 mm) or 4-11/16 in (119 mm), because the difference is 17 mm and it decides the canopy. Measure the plaster opening, which is often wider than the box. Measure the stem, chain or cable where it enters the canopy, since the collar has to pass it and the canopy is drilled to suit. Then note the finish and the ceiling angle. Send those four numbers with a photograph of the ceiling and a supplier can match a canopy without guessing. Ordering by the old canopy diameter alone reproduces the old problem, because the old canopy may have been the part that was wrong.
What our own chandelier listings state
On 4 November 2026 we read the title and description text of all 1,829 active listings in our own admin, 573 of which are chandeliers, and counted the words that decide this purchase. Canopy appears in 18 of the 1,829 listings and in 12 of the 573 chandeliers, which is 2.1 percent. A canopy dimension with a unit appears in 6 of the 573. A base plate is named in 21 of the 573. A ceiling medallion appears in none of the 1,829. Sloped ceiling adaptable is stated for 211 of the 573 chandeliers, 36.8 percent, while a swivel appears in none of them. A chain is named in 212 of the 573. That is the honest picture of what a listing tells a buyer, and it is the list of questions to put to any supplier before ordering.
| What the listing states | Chandeliers (573) | Whole catalogue (1,829) |
|---|---|---|
| Mentions a canopy | 12 (2.1 percent) | 18 (1.0 percent) |
| States a canopy dimension with a unit | 6 (1.0 percent) | 7 (0.4 percent) |
| Names a base plate | 21 (3.7 percent) | 26 (1.4 percent) |
| Names a ceiling medallion | 0 (0.0 percent) | 0 (0.0 percent) |
| States sloped ceiling adaptable | 211 (36.8 percent) | 237 (13.0 percent) |
| Names a swivel | 0 (0.0 percent) | 26 (1.4 percent) |
| Names a chain | 212 (37.0 percent) | 213 (11.6 percent) |
When a canopy swap is not the right choice
A bigger canopy is the wrong purchase in four cases. If the fixture hangs from a box that is loose in the plaster, the fix is the box, and a wider canopy only hides the movement for a while. If the ceiling opening is wider than 150 mm because a fan was removed, patch and skim first; a 200 mm canopy over a patched hole reads as a plaque and draws the eye to the repair. If the fixture is above 20 kg (44 lb), the load question comes before the cover question, and it needs an electrician rather than a part. And if the ceiling is sloped by more than about 15 degrees, a flat canopy in a larger size still stands off, so the part to order is a swivel, not a wider plate. A canopy is a cover. When the problem is the ceiling, the box, or the load, a cover is not the answer, however wide it is.
Numbers and sources
| Number in this page | Value | Source | Nature |
|---|---|---|---|
| Active listings read | 1,829 | Shopify admin, 4 November 2026, all active products | Direct read |
| Variants in those listings | 12,615 | Same read | Direct read |
| Chandeliers | 573 | Same read, productType equals Chandelier | Direct read |
| Canopy mentioned | 12 of 573 / 18 of 1,829 | Same read, word match on canopy in title plus description text with markup stripped | Count, reproducible |
| Canopy plus dimension | 6 of 573 / 7 of 1,829 | Same read, canopy within 60 characters of a number with cm, mm or in | Count, reproducible |
| Base plate named | 21 of 573 / 26 of 1,829 | Same read | Count, reproducible |
| Ceiling medallion named | 0 / 0 | Same read | Count, reproducible |
| Sloped ceiling adaptable | 211 of 573 / 237 of 1,829 | Same read | Count, reproducible |
| Swivel named | 0 of 573 / 26 of 1,829 | Same read | Count, reproducible |
| Chain named | 212 of 573 / 213 of 1,829 | Same read | Count, reproducible |
| Weight stated | 1 of 1,829 | Same read, net weight or gross weight | Count, reproducible |
| 5 in = 127 mm | 127 mm | Unit conversion, 5 times 25.4 | Arithmetic |
| 4 in = 102 mm | 101.6 mm | Unit conversion, 4 times 25.4 | Arithmetic |
| 4-11/16 in = 119 mm | 119 mm | Unit conversion of the trade size | Arithmetic |
| 6 in = 152 mm | 152 mm | Unit conversion, 6 times 25.4 | Arithmetic |
| 3-1/2 in = 89 mm | 89 mm | Unit conversion, 3.5 times 25.4 | Arithmetic |
| Cover per side, 127 mm over 102 mm | 12.7 mm | (127 minus 101.6) divided by 2 | Arithmetic |
| Cover per side, 102 mm over 89 mm | 6.4 mm | (101.6 minus 88.9) divided by 2 | Arithmetic |
| Cover per side, 152 mm over 119 mm | 16.7 mm | (152.4 minus 119.06) divided by 2 | Arithmetic |
| Cover per side, 127 mm over 119 mm | 4 mm | (127 minus 119) divided by 2 | Arithmetic |
| Gap on a 30 degree slope, 127 mm canopy | 73 mm | 127 times tangent of 30 degrees, 0.577 | Arithmetic, geometry |
| Gap on a 45 degree slope, 127 mm canopy | 127 mm | 127 times tangent of 45 degrees, 1.0 | Arithmetic, geometry |
| Slope threshold, about 15 degrees | 15 degrees | Working threshold used on this page, not a standard | Convention |
| Load threshold, about 20 kg (44 lb) | 20 kg | Working threshold used on this page, above which an electrician assesses the brace | Convention |
| Box trade sizes 3-1/2, 4 and 4-11/16 in | 89, 102, 119 mm | US electrical trade sizes as sold; the pairing with canopy size is what installers expect | Trade convention, not a standard |
| Hole wider than 150 mm | 150 mm | Working threshold used on this page for patching rather than covering | Convention |
Box sizes and canopy pairings are US trade conventions, not a published standard, and they are written here as what installers expect rather than as a requirement. The 15 degree slope threshold and the 20 kg load threshold are working thresholds used on this page, not code limits. All catalogue counts were read on 4 November 2026 and describe listing text, not the physical fixture; a canopy can be supplied on request whether or not the listing names one.