How thick is the glass on a 75-gallon aquarium?

Commercially, a 75 (48 × 18 × 21 in) typically ships with 3/8 inch (10 mm) annealed float glass and a glass bottom brace. Our calculator returns ~12 mm minimum with SF=3.8 — manufacturers run leaner because they validate with their specific bracing design. For a DIY build, 12–15 mm is the safe answer.

How thick should glass be on a 120-gallon tank?

A 120-gallon tall (24 in height) needs roughly 15 mm annealed at SF=3.8, or 8 mm tempered. A 120 long (lower height, 21 in) drops to 12 mm annealed.

Is tempered or annealed glass safer?

Tempered is stronger at the same thickness, but if it does fail it shatters catastrophically into pebble-sized chunks — flooding your room. Annealed cracks slowly and gives you warning. Most builders use tempered for the bottom (load-bearing) and annealed for the front (so you can drill if needed).

What's the safety factor used here?

3.8 by default — the Wisner hobby standard, reused by Omni Calculator. You can lower it to 2.5 in the input if you understand the trade-off (less margin against scratches, impact loads, and long-term creep), but anything below 2.5 is asking for trouble.

Is this formula peer-reviewed?

No. The Wisner derivation is community-standard in the aquarium hobby and the basis for most calculators online, including this one. The underlying physics (water pressure × geometry / allowable stress) is standard mechanics of materials. For a tank you'd put against an interior wall in someone else's apartment, hire a structural engineer.

Calculator

Aquarium Glass Thickness Calculator

This is a planning tool for DIY tank builds and a sanity check before you trust a no-name imported tank. It returns the minimum thickness required for the water-pressure load at the bottom seam, using the Wisner-style formula that hobby builders and Omni Calculator both use. The formula is community-standard, not formally peer-reviewed — flagged inside the result.

Glass thickness

Tank length (in)

Tank height (in)

Water depth from base to rim — this drives the pressure load.

Tank width (in)

Glass type

Safety factor

3.8 is the hobby standard (Wisner). Drop to 2.5 only if you know what you're doing.

Minimum thickness

12.10mm

In inches

0.477in

Buy next size up

15mm

Allowable stress: 5.08 MPa

Glass type

annealed

Formula source: Wisner-style hobby derivation [community standard, not formally peer-reviewed]. For loads outside the typical hobby range (height > 36 in or unusual aspect ratios), get an engineering review.

How this is calculated

σ_allow = σ_breaking / SF
t = H × sqrt( P / (2 × σ_allow) )

where:
  P            = ρ × g × H  (water pressure at bottom)
  ρ            = 1000 kg/m³
  g            = 9.80665 m/s²
  σ_breaking   = 19.3 MPa  (annealed float)
                = 77.2 MPa (tempered, 4× annealed)
  SF (default) = 3.8  (Wisner hobby standard)

The breaking strength values are standard glass-industry numbers — Saint-Gobain's annealed float at ~19 MPa modulus of rupture, tempered at 4× that. The safety factor 3.8 is the value Wisner used in his original hobby derivation and is reused by Omni Calculator's aquarium glass thickness tool.

When to buy tempered glass

Most commercial 75-gallon and up rectangular tanks ship with tempered bottom and sometimes tempered sides. Tempered glass survives the same pressure with one-quarter the thickness, which is why thin-walled "rimless" tanks even exist. The trade-off: you can't drill tempered glass after the fact (it shatters into pebbles), so plumb your bulkheads first or buy a tank with the holes already cut.

Starphire / low-iron is not stronger

Low-iron glass (Starphire is the PPG brand name; the generic is "ultra-clear" or "optiwhite") has the same tensile strength as standard annealed float. What you're paying for is the iron-free composition that removes the green tint — clearer viewing, especially on thick panes. The calculator treats it as annealed for thickness purposes.

When this formula is wrong

For tanks taller than 36 in (91 cm), unusual aspect ratios (long thin lap pools), or any tank holding livestock you care about deeply, get an engineering review. The Wisner formula was derived for typical rectangular hobby tanks under static water load — it assumes the long edges are silicone-bonded to perpendicular braces, doesn't account for euro-bracing differently than full top trim, and ignores fatigue cycling from temperature swings.

FAQ

How thick is the glass on a 75-gallon aquarium?: Commercially, a 75 (48 × 18 × 21 in) typically ships with 3/8 inch (10 mm) annealed float glass and a glass bottom brace. Our calculator returns ~12 mm minimum with SF=3.8 — manufacturers run leaner because they validate with their specific bracing design. For a DIY build, 12–15 mm is the safe answer.
How thick should glass be on a 120-gallon tank?: A 120-gallon tall (24 in height) needs roughly 15 mm annealed at SF=3.8, or 8 mm tempered. A 120 long (lower height, 21 in) drops to 12 mm annealed.
Is tempered or annealed glass safer?: Tempered is stronger at the same thickness, but if it does fail it shatters catastrophically into pebble-sized chunks — flooding your room. Annealed cracks slowly and gives you warning. Most builders use tempered for the bottom (load-bearing) and annealed for the front (so you can drill if needed).
What's the safety factor used here?: 3.8 by default — the Wisner hobby standard, reused by Omni Calculator. You can lower it to 2.5 in the input if you understand the trade-off (less margin against scratches, impact loads, and long-term creep), but anything below 2.5 is asking for trouble.
Is this formula peer-reviewed?: No. The Wisner derivation is community-standard in the aquarium hobby and the basis for most calculators online, including this one. The underlying physics (water pressure × geometry / allowable stress) is standard mechanics of materials. For a tank you'd put against an interior wall in someone else's apartment, hire a structural engineer.

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Sources & references

01
Omni Calculator — Aquarium glass thickness
https://www.omnicalculator.com/other/aquarium-glass-thickness
02
MonsterFishKeepers — Glass thickness reference chart
https://www.monsterfishkeepers.com/forums/threads/diy-aquarium-glass-thickness-calculator.27786/
03
Saint-Gobain — Planiclear annealed float glass spec
https://www.saint-gobain-glass.com/en/products/sgg-planiclear

Last reviewed 2026-05-25