120 Gallon Aquarium dimensions
The classic 120 is a 4 ft × 2 ft × 2 ft box — deep front to back, which is why reef keepers like it. Dimensions and weights are Marineland's published figures; a 5 ft “120 XH” variant is listed too.
Measuring your own tank? The rectangular tank volume calculator works out gallons at any water depth.
| Spec | Value |
|---|---|
| Length | 48 in |
| Width | 24 in |
| Height | 24 in |
| Geometric capacity | 119.7 gal |
| Nominal rating | 120 gal |
| Liquid weight (brim-full) | 999 lb of water |
| Empty tank weight (manufacturer) | 144 lb |
| Full weight (manufacturer) | 1,104 lb |
Nominal rating versus real geometry
Rated 120 gal. Computed from the dimensions in the table above: 119.7 gal. The geometry comes out 0.3 gallons short of the label — 0.3 %. Published exterior dimensions and internal volume are not the same thing, and glass thickness and the trim account for most of the gap.
Other footprints sold under this rating
| Model | L × W × H | Geometric |
|---|---|---|
| Marineland 120 Corner-Flo (item 97008; 144 lb empty, 1,104 lb full) | 48 × 24 × 24 in | 119.7 gal |
| Marineland 120 XH Corner-Flo (items 97010, 97026; 157 lb empty, 1,157 lb full) | 60 × 18 × 26 in | 121.6 gal |
| Custom Aquariums 120 (⅜ in glass; 110 gal actual) | 48 × 24 × 24 in | 119.7 gal |
A rating names a size class, not a box: check which footprint you have before sizing a stand, a lid or a canopy.
What this weighs on your floor
| Water, brim full | 999 lb |
| Plus glass, substrate, rock and stand (≈ 25 % allowance) | ≈ 1,248 lb gross |
| Footprint | 48 in × 24 in = 8 ft² |
| Load over its own footprint | ≈ 156 lb/ft² |
| IRC design live load, habitable room (not a bedroom) | 40 lb/ft² |
| IRC design live load, sleeping room | 30 lb/ft² |
That is roughly 3.9× the 40 lb/ft² design live load in IRC Table R301.5, over the tank's own footprint — what that does and does not mean is set out in the aquarium reference.
What is the same for every tank of this kind (floor loading, from rated size to actual water volume, what governs an aquarium's rated size) is set out once on the sizes hub, in the aquarium reference and the common questions for every tank.
Dimension drawing
FAQ
What are the dimensions of a 120 gallon aquarium?
Marineland lists its 120 Corner-Flo (item 97008) at 48 × 24 × 24 in (length × width × height, exterior). Other makers' tanks with the same rating can differ by an inch or so — check your tank's label or spec sheet.
How much does a full 120 gallon aquarium weigh?
About 999 lb of water filled to the brim, before the glass, substrate, rock and stand. With a typical allowance for those, plan for roughly 1,248 lb.
How many gallons does a 120 gallon aquarium really hold?
Brim-full, the exterior dimensions give 119.7 gal. In use, with an inch of air gap and a substrate bed, expect several gallons less — enter your own water depth in the rectangular tank volume calculator.
Sources and standards
- Corner-Flo Aquariums — Specifications and Sizes (2012)Marineland / Spectrum Brands (manufacturer)https://sc10cdn.spectrumbrands.com/-/media/project/spectrumcommerce/marineland/files/product-files/aquarium-products/tanks/corner-flo-aquariums-specs-and-sizes-charts.pdf“120 Black 1 48" x 24" x 24" 144 lbs. 1104 lbs. 97008” and “120XH Black 2 60" x 18" x 26" 157 lbs. 1157 lbs.”
- 120 Gallon 24″H × 48″L × 24″D Glass Aquarium — product specificationsCustom Aquariums (manufacturer)https://www.customaquariums.com/product/120-gallon-24h-x-48l-x-24d-glass-aquarium-basic-package/“Model Gallons 120 / Actual Gallons 110”; ⅜ in glass.
- Handbook 44, Appendix C — General Tables of Units of MeasurementNational Institute of Standards and Technology, U.S. Department of Commercehttps://www.nist.gov/document/2026-nist-handbook-44-appendix-c
- International Residential Code, Table R301.5 — Minimum uniformly distributed live loadsInternational Code Council (free read-only access at codes.iccsafe.org)https://codes.iccsafe.org/s/IRC2021P2/chapter-3-building-planning/IRC2021P2-Pt03-Ch03-SecR301.5
- Methodology — the partial-fill formulas and liquid densities used on this sitetankvolumecalc.comhttps://tankvolumecalc.com/methodology/
Every linked source above was retrieved and checked on 2026-11-01.