Fish Tank Glass Thickness Calculator

Aquarium Glass Thickness Calculator

Enter your water depth and longest panel, choose rimless or braced, and get a stocked-size glass thickness in millimeters or inches — plus the standard thickness chart, a five-piece cut list, and the filled weight of the finished tank. Built for DIY builders; no sign-up, no cost.

🛠️ Build: DIY rimless & braced⏱️ Setup time: ~12 min📊 Difficulty: beginner-friendly

Planted rimless glass aquarium with clear water on a wooden stand

Measure the water, size the glassPhoto: Unsplash

Fish Tank Glass Thickness Calculator

Longest panel length (cm)

Tank width (cm)

Water depth (cm)

Water type

Safety factor

Construction

Annealed glass

12 mm

≈ 1/2" · raw minimum 10.2 mm

If tempered

6 mm

≈ 3/16" · cannot be cut later

Inputs in play

Depth 45 cm · ratio 2
Freshwater · SF 3.8 · rimless

Your 5-piece glass cut list

Panel	Cut size (cm)	Pieces
Bottom	90 × 45 cm at 12 mm	1
Front	90 × 45 cm at 12 mm	1
Back	90 × 45 cm at 12 mm	1
Left side	42.6 × 45 cm at 12 mm	1
Right side	42.6 × 45 cm at 12 mm	1

Glass weight: 48 kgWater: 168 LFilled tank: ≈ 216 kg

Tip: depth beats height

Calculate from the waterline, not the rim. A tank filled 3 cm below its edge asks for measurably less glass than one filled to the brim — and overflow braces change the waterline, not the panel.

Warning: water is relentless

Water pressure is a permanent load that never takes a day off. Glass that survives a year can still fail in year three if the safety factor was guessed instead of chosen — 3.8 exists because failures are slow-motion and total.

Don't: mix build styles

Never order glass for a braced calculation and then assemble it rimless "because it looked better." The thickness answer and the construction style are a package — changing one invalidates the other.

Step-by-Step Build SOP

How to Calculate Aquarium Glass Thickness, Start to Finish

Six steps take you from an empty room to an order-ready glass specification — about 12 minutes end to end. The two steps marked critical are where DIY builds most often go wrong; the checklist below tracks your progress as you go.

Build progress0/7 verified · 0%

Measure the water depth, not the tank height

2 minCritical Step

The panel is stressed by the water column pressing on it, so the number that matters is from the inside bottom of the tank to the planned waterline — usually 2–3 cm below the rim. If the tank will sit on a stand that tilts even slightly, the effective depth at the deep end rises; add 1 cm of margin if your stand is adjustable rather than level-locked.

✓ Success check: Depth measured inside the tank, to the waterline, not the glass top edge.

Measure the panel length and get the aspect ratio

2 minVerification

Measure the longest single glass panel — on most tanks that is the front or back. Divide its length by the water depth to get the aspect ratio. A 90 × 45 × 45 tank has a 90 cm front panel over 45 cm of water, a ratio of 2.0. Long, shallow panels bend more than square ones, which is why the calculator asks for both numbers.

✓ Success check: Ratio = longest panel ÷ water depth, written down.

Choose rimless or braced construction

1 minVerification

Rimless (braceless) tanks have open tops — the glass is elegant and the light entry is superb, but each panel loses the support a top brace gives it. Braced tanks add a cross-brace or an external rim strip that shortens the unsupported span. The same tank in rimless form needs roughly 15–20% more thickness than braced.

✓ Success check: Construction style picked before touching the safety factor.

Pick the safety factor for your livestock

1 minCritical Step

The standard aquarium safety factor is 3.8, and it is what most commercial tanks are built to. Saltwater and reef systems carry denser water and irreplaceable livestock, so 4.5 is the responsible choice. Large tanks over 400 liters, tanks with children or offices beneath them, and arowana or monster-fish builds deserve 5.0.

✓ Success check: Safety factor matches water type and what failure would actually cost.

Read the thickness and round up to a stocked size

1 minVerification

The calculator returns the raw minimum and the nearest stocked size — glass is sold in 4, 5, 6, 8, 10, 12, 15, 19, and 25 mm. Always build with the stocked size at or above the raw number, never between sizes. If you are tempering the panels instead, halve the raw number — but order all panels tempered up front, because tempered glass cannot be cut or drilled later.

✓ Success check: Stocked thickness ≥ raw calculated minimum.

Verify with the cut list and the filled weight

5 minVerification

Before ordering, generate the five-piece cut list and check the filled weight of the finished tank against your floor and stand. A 120 × 50 × 50 tank weighs about 367 kg filled — the stand and the floor joists need to know that number, not just you. This verification step catches sizing errors while they are still free to fix.

✓ Success check: Cut list matches tank plan; floor and stand rated above filled weight.

Pre-Order Checklist

Reference Chart

Aquarium Glass Thickness Chart for Standard Tank Sizes

The chart below applies the same model as the calculator — water depth, aspect ratio, 3.8 safety factor, round up to a stocked size — to the tank dimensions people actually build. Read the rimless column if you want the open-top look; read the braced column if you will add a center brace or a rim strip. Freshwater figures; add roughly half a stock size when running saltwater at SF 4.5.

Tank (L × W × H cm)	Volume	Nearest inch	Braced	Rimless
30 × 30 × 30 cm	27 L	3/16"	4 mm	5 mm
40 × 40 × 40 cm	64 L	5/16"	6 mm	8 mm
60 × 30 × 36 cm (60P)	65 L	1/4"	6 mm	8 mm
90 × 45 × 45 cm	182 L	3/8"	10 mm	12 mm
120 × 45 × 45 cm	243 L	3/8"	10 mm	12 mm
120 × 50 × 50 cm	300 L	1/2"	12 mm	15 mm
150 × 60 × 60 cm	540 L	5/8"	15 mm	19 mm
180 × 60 × 60 cm	648 L	3/4"	15 mm	19 mm

Notice the pattern in the chart: thickness follows the water depth more than the tank length. A 120 × 45 × 45 and a 90 × 45 × 45 share a depth, so their braced walls land a single stock size apart — while a 120 × 50 × 50, only 5 cm deeper, jumps a full size. Depth is cubed inside the bending equation; length only feeds the aspect ratio.

Row of rimless glass aquariums of different sizes on racks in a fish store

Same water, different spans — depth drives thicknessPhoto: Unsplash

Rimless vs Braced: How Bracing Changes the Thickness Answer

The single biggest fork in any aquarium glass thickness calculation is whether the top of the tank is open or tied together. Water pressure pushes each panel outward; what resists that push is the panel's stiffness and whatever its edges are attached to. Braces are cheap stiffness. Rimless is expensive elegance.

🪞 Rimless / braceless tanks

Every panel has a free top edge — the bending coefficient rises ~35%, so glass goes up one to two stock sizes.
Unbroken sightlines and full light penetration — the reason planted and reef builders pay the glass premium.
Assembly tolerance is tighter: without a rim forcing squareness, panel edges must meet accurately during silicone cure.
Evaporation is unhidden and jumpers are unblocked — a lid is an accessory you will actually want.

🔩 Braced tanks

A center brace or rim strip ties opposite walls together, roughly halving the unsupported span of long front panels.
The thickness answer drops one to two stock sizes versus rimless — the quiet reason most mass-market tanks have rims.
Braces cast shadow lines under LED strips; position lights between braces or accept the striping.
Plastic rim frames also protect top edges during transport and water changes — practical, if less photogenic.

The half-brace compromise: long tanks (120 cm and up) often run a single center brace instead of a full perimeter rim. That halves the front panel's span and lets a 120 × 45 × 45 build stay at 10 mm instead of stepping to 12 mm — but the brace must be structural silicone and glass, not a plastic clip. If you plan a removable brace for equipment access, calculate as rimless and keep the margin.

Annealed vs Tempered Glass for Aquariums

Tempering reheats annealed glass to near softening and quenches it, locking the outer surfaces in compression. That compression is what buys the strength: a tempered panel bends roughly four to five times harder before it fails, so the calculator halves its thickness — a 12 mm annealed wall becomes a 6 mm tempered one with the same safety factor. Weight drops, clarity is unchanged, and scratch resistance improves.

What tempering costs you matters more for a tank than for a table top. Tempered glass cannot be cut, drilled, or edged after the quench — every hole for bulkheads and every dimension must be final before tempering. And it fails differently: annealed glass cracks from a scratch or a stress riser and leaks gradually, often overnight, giving you hours of warning; tempered glass detonates into fragments in seconds. For a tank sitting on a carpeted floor above a finished basement, that difference in failure mode is the whole decision.

Property	Annealed	Tempered
Bending strength	1× (baseline)	4–5× — thickness halves
Failure mode	Slow crack, gradual leak	Instant, full fragmentation
Cutting after purchase	Yes — cut, drill, polish freely	No — factory dimensions are final
Wall thickness (90×45×45 rimless)	12 mm	6 mm
Cost per panel	Baseline	+60–120% depending on region
Scratch resistance	Standard	Higher surface hardness

The pragmatic middle path used by experienced builders: annealed walls (graceful failure, easy fixes) with a tempered or laminated bottom panel where point loads from rocks and equipment concentrate. If you temper everything, buy a spare bottom panel at the same time — a shattered base is a full teardown, and the remelt lead time at most shops is two to three weeks.

How Much Does a Filled Tank Weigh?

Thickness decides whether the glass survives; weight decides whether your floor does. Water is the heavyweight — 1 kg per liter — and the glass adds its own share at 2.5 kg per liter of glass volume. The table pairs each chart tank with its glass weight at the recommended thickness and its filled weight in freshwater (add ~2.5% for saltwater).

Tank (cm)	Glass only	Water only	Filled total
30 × 30 × 30	5.4 kg	24 kg	≈ 29 kg
40 × 40 × 40	17.6 kg	60 kg	≈ 78 kg
60 × 30 × 36	15.7 kg	62 kg	≈ 78 kg
90 × 45 × 45	44 kg	174 kg	≈ 218 kg
120 × 45 × 45	58.7 kg	232 kg	≈ 291 kg
120 × 50 × 50	81 kg	286 kg	≈ 367 kg
150 × 60 × 60	144 kg	514 kg	≈ 658 kg
180 × 60 × 60	172.8 kg	617 kg	≈ 790 kg

Two numbers people forget: the stand must carry the filled weight with margin (a level, rim-supported stand spreads 300 kg across its posts; a 浮浮 stand loads two corners), and the floor matters above ground level — a 540 L tank on a wooden joist floor deserves a quick check against joist direction and span before, not after, the first fill.

Marine & Reef Tanks: Why the Safety Factor Climbs

Saltwater raises the stakes twice. First, physics: dissolved salt pushes density to about 1,025 kg/m³ — a 2.5% pressure increase that alone would barely move the thickness answer. Second, and decisively, consequence: a reef system holds thousands of dollars of coral and fish, a refugium above the display, and salinated water that ruins drywall and carpet on contact. The standard response across the hobby is a 4.5 safety factor for marine builds, which the calculator applies from the dropdown.

Reef-specific habits that earn their keep: over-sizing the sump and bottom pane (the display drains there and the bottom carries rock stacks), keeping live rock off the glass with egg-crate or支架 stands so no point load touches a panel, and adding an auto-top-off so salinity — and therefore density — stays stable instead of creeping upward between manual top-offs. A large arowana or monster-fish tank deserves the same 4.5 factor plus a glass lid: a 60 cm fish hitting a panel in a turn is an impact load no static calculation models, and lids absorb it.

Public-display rule of thumb: public aquaria design to factors of 5 and beyond because failure costs are counted in litigation and livestock worth more than the tank. A home builder who adopts SF 5.0 on a display tank buys the same margin for the price of one extra stock size of glass.

Acrylic vs Glass: When the Calculator Does Not Apply

Acrylic (PMMA) solves problems glass cannot: it weighs half as much per panel, it bonds optically clear so seams vanish, it can be routed and formed, and it insulates ~20% better. But its stiffness is the catch — acrylic flexes about 30 times more than glass for the same thickness, so acrylic tank walls are designed by deflection limits, not stress, and large acrylic builds run thickerthan glass equivalents, not thinner. A 60 cm cube in acrylic wants 10–12 mm where glass wants 6–8 mm; a 2 m viewing panel in acrylic may need 40 mm of cell-cast sheet.

Choose acrylic when

• The build needs drilled bulkheads near edges or odd shapes
• Weight limits matter (upper floors, stands near their rating)
• Impact risk is real (public, kids, large cichlids)

Choose glass when

• Rigidity and scratch resistance lead the priority list
• Budget is fixed — glass stays cheaper at every size
• The tank is a standard rectangle within this chart's range

Acrylic also scratches more easily than glass — though fine scratches can be polished out, which glass forgives never. The calculator on this page is glass-specific by design; treat any acrylic answer from a glass tool as a starting point for a conversation with the sheet supplier, who will size by their own deflection tables.

Budgeting the Build: What the Glass Will Cost

Glass price scales with area × thickness, so the cut list is a shopping list. As regional ballparks for cut-and-edged float glass: standard clear glass runs roughly $8–15 per m² per millimeter of thickness in North America, £7–12 in the UK, and A$10–18 in Australia; low-iron glass commands a 40–80% premium; tempering adds 60–120%. A 90 × 45 × 45 rimless build in standard glass needs about 1.3 m² of 12 mm — call it $130–230 in North America before silicone, primer, and edge polishing.

Three budget traps: low-iron creep (upgrading all five panels instead of just the front doubles the premium — most builders upgrade front and sides only), polished edges on panels nobody sees (the bottom and back can ship raw-cut and save 10–15%), and delivery minimums(glass shops often charge a flat $40–80 delivery that makes two orders cost double — order everything, including the spare bottom, at once). For a full cost breakdown with regional tables, the glass price calculator estimates cut-to-size cost including edge work and wastage.

Aquarium Glass Thickness FAQ

How do I calculate aquarium glass thickness?▼

Multiply the water depth by itself three ways: thickness scales with roughly the square root of depth cubed times the safety factor, divided by the design strength of the glass. In practice you enter the water depth and the longest panel length into the calculator above, pick rimless or braced, and it applies the plate-bending model with the 3.8 safety factor for you — then rounds up to the nearest stocked size of 4, 5, 6, 8, 10, 12, 15, 19, or 25 mm.

How thick should glass be for a 40 cm cube tank?▼

A 40 × 40 × 40 cm cube needs 6 mm braced or 8 mm rimless at the standard 3.8 safety factor. With saltwater and the marine factor of 4.5, the rimless answer rises toward 10 mm. The tank holds about 64 liters and weighs roughly 78 kg filled — light enough for most floors, which is exactly why 40 cm cubes are the most popular DIY size.

Why do rimless tanks need thicker glass than braced tanks?▼

A top brace ties the front, back, and side panels to each other, shortening the unsupported span that water pressure can bend. Remove the braces and each panel carries its load with a free top edge, which raises the bending stress by about a third. The calculator compensates with a rimless penalty factor of 1.35 on the bending coefficient — the reason a 60 × 30 × 36 tank moves from 6 mm braced to 8 mm rimless.

Is tempered glass better for aquariums?▼

Tempered glass is roughly four to five times stronger in bending, so the calculator can halve the thickness — a 12 mm annealed wall becomes a 6 mm tempered one. The trade-offs are real, though: tempered panels cannot be cut, drilled, or reworked after tempering, they fail suddenly into small fragments rather than cracking slowly, and they cost noticeably more. Most builders keep walls annealed for graceful failure and use tempered only where scratch resistance or slim profiles matter.

What safety factor should a marine or reef tank use?▼

Use 4.5 for saltwater. Reef water is about 2.5% denser than fresh, which raises the pressure slightly, but the real reason is consequence: a saltwater failure dumps 200-plus liters of salinated water into a living room and usually kills the entire system. Commercial reef-ready tanks frequently carry explicit 4.5 factors, and the calculator applies the density difference (1,025 kg/m³) automatically when you pick saltwater.

How much does a filled aquarium weigh?▼

Water weighs almost exactly 1 kg per liter, glass about 2.5 kg per liter of glass volume, so a rough rule is: filled weight ≈ water volume + glass weight, and the glass adds 15–25% on small tanks and under 10% on large ones. The weight table on this page lists common sizes — a 90 × 45 × 45 comes in around 218 kg, and a 150 × 60 × 60 at roughly 658 kg including the glass.

Can I use the calculator in inches?▼

Yes — switch the unit toggle to inches and every field converts: enter 36 inches of water depth and a 48 inch front panel and the calculator returns the same answer as the metric equivalents, quoted both in millimeters and in fractional inches (6 mm ≈ 1/4 inch, 10 mm ≈ 3/8 inch, 12 mm ≈ 1/2 inch). The underlying model always computes in metric; the toggle just translates your inputs.

Why is my calculated thickness different from my pet shop tank?▼

Commercial tanks are built to pass cost review as well as physics: mass-market brands often sit at the thin end of the allowed range, add center braces, and use polished edges, while quality rimless brands run thicker glass with low-iron panels. A DIY tank has no factory jig holding it square during assembly, so building one stock size above the commercial equivalent is the standard hedge — the calculator's round-up rule exists precisely for this.

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Sizing a window or a panel instead of a tank? The homepage glass weight calculator weighs any panel shape from its dimensions, and the glass load calculator covers dry-side bending and spans. Tank-specific resources: glass performance calculator and glass price calculatorround out the toolkit.

Size the Glass, Then Build With Confidence

Twelve minutes of measuring and one safety-factor decision stand between a sketch and an order sheet. Run the calculator, print the cut list, and check the filled weight before the glass shop does — free, instant, and private.

Back to the thickness calculator