Bracket spacing — not shelf length — decides everything. Enter the span, depth, thickness and support style, and read the kilograms your shelf really holds, which limit wrote the number, and six scenario builds showing the spec that fits before you order the glass.
Span sets the limit — thickness answers itPhoto: UnsplashHolds (distributed)
139 kg
= 307 lb spread over the shelf
Per running metre
232 kg/m
the figure bracket ratings are matched against
Governing limit
Breakage
sag at full load: 4.3 mm (limit span/100)
The result is a distributed load — jars in a row, books along the shelf. A single heavy object in the centre cuts usable capacity roughly in half, and for shelves that stay loaded for years, keep the live load under a quarter of this number (static fatigue). Design stress assumed: 32 MPa tempered.
Each card is the calculator's arithmetic applied to a job people actually bring to the shop — with the guess that usually gets made and the spec that survives contact with reality. Tick what you are shelving to spotlight the matching cards.
600 × 300 mm · 8 mm tempered · 2 end brackets
139 kgcapacity (stress-governed)
✕ Guess: 6 mm annealed over a 600 mm gap — sag becomes permanent
✓ Spec: 8 mm tempered on 2 pins: 171 kg capacity, ~6% used by a full row
800 × 300 mm · 10 mm tempered · 2 end brackets
163 kgcapacity (stress-governed)
✕ Guess: Bought by cabinet size, not by jar weight — 800 mm is a long glass span
✓ Spec: 10 mm tempered: 160 kg capacity; a full jar row is ~25 kg
500 × 150 mm · 6 mm tempered · 2 end brackets
47 kgcapacity (stress-governed)
✕ Guess: 3 mm ‘picture glass’ — holds towels until the first hot steam cycle
✓ Spec: 6 mm tempered: 46 kg capacity, humidity-proof and towel-safe
1219 × 305 mm · 10 mm tempered · 2 end brackets
94 kgcapacity (sag-governed)
✕ Guess: Stock 10 mm rated by area tables, then braced at 48 in — sag kills the look
✓ Spec: 10 mm tempered full span holds ~95 kg; center bracket lifts it past 130 kg
1000 × 350 mm · 12 mm tempered · 2 end brackets
219 kgcapacity (stress-governed)
✕ Guess: Assuming the 12 mm sheet spans a metre on two pins by feel
✓ Spec: 12 mm tempered: 215 kg capacity — amplifiers are a rounding error
300 × 300 mm · 6 mm annealed · 3+ brackets / rail
78 kgcapacity (stress-governed)
✕ Guess: Short spans tempt people to skip tempering — then a bottle taps the edge
✓ Spec: 6 mm annealed on a rail: 95 kg capacity at 300 mm; tempered doubles the edge safety
Kilograms of distributed load per 300 mm-deep shelf on two end brackets, computed live from the same model — annealed and tempered side by side. The * marks cells where sag, not breakage, sets the number: the shelf will bend visibly before it is ever at risk, which is a buying decision, not a safety one.
| Thickness | 300 mm span | 400 mm span | 600 mm span | 800 mm span | 1000 mm span |
|---|---|---|---|---|---|
| Tempered (32 MPa) | |||||
| 4 mm | 70 kg | 52 kg | 24 kg * | 14 kg * | 9 kg * |
| 6 mm | 157 kg | 117 kg | 78 kg | 46 kg * | 30 kg * |
| 8 mm | 278 kg | 209 kg | 139 kg | 104 kg | 70 kg * |
| 10 mm | 435 kg | 326 kg | 217 kg | 163 kg | 130 kg |
| 12 mm | 626 kg | 470 kg | 313 kg | 235 kg | 188 kg |
| Annealed (8 MPa) | |||||
| 4 mm | 17 kg | 13 kg | 9 kg | 7 kg | 5 kg |
| 6 mm | 39 kg | 29 kg | 20 kg | 15 kg | 12 kg |
| 8 mm | 70 kg | 52 kg | 35 kg | 26 kg | 21 kg |
| 10 mm | 109 kg | 82 kg | 54 kg | 41 kg | 33 kg |
| 12 mm | 157 kg | 117 kg | 78 kg | 59 kg | 47 kg |
* Sag-governed cell — capacity is capped at span/100 deflection, so add a bracket or step up a thickness. Read the ladder honestly: 6 mm tempered at 800 mm holds 31 kg, and 8 mm at the same span holds 96 kg — the 33% thickness increase bought 3× the capacity, the thickness-squared law in action.
1/8-inch — 3 mm — is the most-searched shelf thickness and the most misjudged. It is genuine furniture glass, sold everywhere, and it is one shop step away from being dangerous above eye level. The ladder below is the whole truth of the 150 mm-deep 1/8-inch shelf: kilograms of distributed load by span.
| Span | Annealed | Tempered |
|---|---|---|
| 200 mm | 7.3 kg | 29.4 kg |
| 300 mm | 4.9 kg | 19.6 kg |
| 450 mm | 3.3 kg | 9.1 kg |
| 600 mm | 2.4 kg | 5.1 kg |
Where 1/8-inch belongs
Cabinet inserts, photo ledges, curio backs, spice racks — spans under 300 mm, loads under 5 kg, nothing above head height.
Where it does not
Bookshelves (a single row of paperbacks doubles its 450 mm capacity), bathroom walls, and anywhere a bump is plausible — 3 mm breaks into blades.
The weight itself
A 1/8-inch sheet weighs 7.5 kg/m² (1.54 lb/ft²) — a 600 × 300 shelf is 1.35 kg before anything sits on it. The 1/8-inch glass weight load question is usually answered by the brackets, not the glass.
Edge quality dominates at 3 mm: strength lives and dies at the arris, so polished edges are not cosmetic here. And since 3 mm tempered cannot be drilled afterwards, specify clip-on brackets that grip without holes — the same temper-before-machining rule the load calculator enforces for structural panels.
The 48 × 12 inch (1219 × 305 mm) shelf is the standard retail and wardrobe display size, and it is the case where bracket count changes everything. Three bracket plans, one sheet of 10 mm tempered glass, all numbers from the same model:
Two end brackets — full 1219 mm span
95 kg
≈ 80 kg/m of edge. Sag-governed at 12 mm bow; fine for garment displays and décor, marginal for dense product rows.
Three brackets — two 610 mm spans
190 kg
Halving the span doubles the load twice over in theory; in practice the numbers come back to ~2× once sag is accounted for. Sag drops to 3 mm.
Four brackets — three 406 mm spans
285 kg
Stress-governed now: at 406 mm the 10 mm sheet could take 285 kg before sag even registers. The bracket rail becomes the weakest link, not the glass.
The purchase order implications are worth spelling out: same glass, same shelf, three different shelving systems. Bracket hardware is cheap relative to glass upgrades — a set of three brackets versus two often costs less than the step from 8 mm to 10 mm, and the capacity gain is larger. When a supplier quotes a "48-inch rated" shelf, ask which of these three plans the rating assumes; that single question separates real load ratings from marketing ones.
💡 Tip: cut the span before you thicken the glass
A mid-span bracket roughly doubles capacity and quarters the sag; the equivalent in thickness usually costs 30–50% more on the sheet price. Hardware first, thickness second — the calculator's support selector exists to price that trade in one click.
⚠️ Warning: bracket grip is a load path, not a detail
Shelf capacity means nothing if the bracket tears out of the wall — a 40 kg capacity shelf on hollow drywall anchors is a 5 kg shelf with extra steps. Match the fixing to the wall (studs, masonry anchors, rail systems), and read the bracket rating against the per-metre figure the calculator gives.
❌ Don't: drill tempered glass for brackets
Tempering must happen after all cutting and drilling — a tempered panel drilled in the garage detonates, usually in the frame. Order the finished size with holes and notches specified, and use clip or pin brackets that need no holes at all. The same irreversible-temper rule is why the load calculator refuses to "add a centre support" to a tempered panel after the fact.
The numbers assume a uniformly distributed load on a simply supported strip with polished edges, E = 70 GPa, and the design stresses printed on the type buttons. Point loads halve the answer; chipped or unpolished edges can do worse; very humid rooms (above showers, in unheated garages) justify keeping utilisation low because slow edge crack growth accelerates with moisture and stress together.
For household and retail shelving this model is comfortably conservative. For commercial racking, heavy merchandising walls, or anything glass above people, take the print-out to a glazing engineer — and match the wall fixings to the load, because the glass rarely fails first.
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Related: the glass load calculator runs the parent model for any panel — balustrades, table tops, tank lids — while this page tunes it to bracket-supported shelves. The glass table top calculator covers the full-support case where the base carries everything, and the main weight calculator answers the pure "how heavy is this sheet" question behind every bracket decision.
Sixty seconds of inputs beats a shelf that sags by Christmas or a sheet you paid too much to over-thicken. Run your span, try the bracket plans, and order with the capacity printed in kilograms.
Back to the shelf calculator