Aquarium Glass Thickness and Volume Loss

10 gal 20 × 10 × 12 in exterior · 10.39 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	19.76 × 9.76 × 11.88	9.93 gal	0.46 gal	4.5%
6 mm	19.53 × 9.53 × 11.76	9.47 gal	0.91 gal	8.8%
10 mm	19.21 × 9.21 × 11.61	8.89 gal	1.50 gal	14.4%
12 mm	19.06 × 9.06 × 11.53	8.61 gal	1.78 gal	17.1%

20 gal High 24 × 12 × 16 in exterior · 19.95 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	23.76 × 11.76 × 15.88	19.22 gal	0.73 gal	3.6%
6 mm	23.53 × 11.53 × 15.76	18.51 gal	1.44 gal	7.2%
10 mm	23.21 × 11.21 × 15.61	17.58 gal	2.36 gal	11.9%
12 mm	23.06 × 11.06 × 15.53	17.13 gal	2.82 gal	14.1%

20 gal Long 30 × 12 × 12 in exterior · 18.70 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	29.76 × 11.76 × 11.88	18.01 gal	0.69 gal	3.7%
6 mm	29.53 × 11.53 × 11.76	17.33 gal	1.37 gal	7.3%
10 mm	29.21 × 11.21 × 11.61	16.46 gal	2.24 gal	12.0%
12 mm	29.06 × 11.06 × 11.53	16.03 gal	2.67 gal	14.3%

29 gal 30 × 12 × 18 in exterior · 28.05 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	29.76 × 11.76 × 17.88	27.10 gal	0.95 gal	3.4%
6 mm	29.53 × 11.53 × 17.76	26.18 gal	1.88 gal	6.7%
10 mm	29.21 × 11.21 × 17.61	24.97 gal	3.09 gal	11.0%
12 mm	29.06 × 11.06 × 17.53	24.37 gal	3.68 gal	13.1%

40 Breeder 36 × 18 × 17 in exterior · 47.69 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	35.76 × 17.76 × 16.88	46.43 gal	1.26 gal	2.6%
6 mm	35.53 × 17.53 × 16.76	45.19 gal	2.50 gal	5.2%
10 mm	35.21 × 17.21 × 16.61	43.57 gal	4.12 gal	8.6%
12 mm	35.06 × 17.06 × 16.53	42.78 gal	4.91 gal	10.3%

55 gal 48 × 13 × 21 in exterior · 56.73 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	47.76 × 12.76 × 20.88	55.11 gal	1.62 gal	2.8%
6 mm	47.53 × 12.53 × 20.76	53.52 gal	3.21 gal	5.7%
10 mm	47.21 × 12.21 × 20.61	51.43 gal	5.29 gal	9.3%
12 mm	47.06 × 12.06 × 20.53	50.41 gal	6.32 gal	11.1%

75 gal 48 × 18 × 21 in exterior · 78.55 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	47.76 × 17.76 × 20.88	76.70 gal	1.85 gal	2.4%
6 mm	47.53 × 17.53 × 20.76	74.88 gal	3.67 gal	4.7%
10 mm	47.21 × 17.21 × 20.61	72.49 gal	6.05 gal	7.7%
12 mm	47.06 × 17.06 × 20.53	71.32 gal	7.23 gal	9.2%

125 gal 72 × 18 × 22 in exterior · 123.43 gal

Glass	Interior L × W × H (in)	Interior volume	Loss	Loss %
3 mm	71.76 × 17.76 × 21.88	120.76 gal	2.67 gal	2.2%
6 mm	71.53 × 17.53 × 21.76	118.12 gal	5.31 gal	4.3%
10 mm	71.21 × 17.21 × 21.61	114.65 gal	8.78 gal	7.1%
12 mm	71.06 × 17.06 × 21.53	112.94 gal	10.49 gal	8.5%

Which thickness applies to my tank?

Look at the top edge of a side panel; a ruler across the rim reads the thickness directly. Framed tanks under 30 gallons are usually 5 or 6 mm, 40 to 75 gallons 8 to 10 mm, 90 gallons and up 12 mm or more. Rimless tanks skip a size up for stiffness. Acrylic is typically thicker again but is a different material with its own tables.

Why the percentage falls as tanks get bigger

Glass volume grows with surface area while water volume grows with the cube of size, so the glass is a smaller share on large tanks for the same thickness. Larger tanks use thicker glass, which pushes the share back up, so in practice the loss stays in a 5 to 10 percent band across the range.