What Size Aquarium Should You Buy? A Guide to UNS Rimless Tanks

Introduction

UNS tank names look like a filing system nobody explained. A 60S, a 60U and a 60L are all called "60" and hold 10, 20 and 6 gallons respectively. A 45S is five gallons; a 45T is eleven. Then there is the T series and the Prism series on top of that. It is genuinely confusing, and the store listings do not decode it for you.

The good news is that the system is completely logical once you know the two rules. This guide breaks down what the numbers and letters mean, gives you a size table you can actually compare against, and covers how to choose by the space you have and by what you want to grow.

Rule One: The Number Is Length in Centimetres

Every UNS model number is the tank's length in centimetres. Not gallons, not a model year — length.

• 30 = 30cm ≈ 11.8 inches
• 45 = 45cm ≈ 17.7 inches
• 60 = 60cm ≈ 23.6 inches
• 75 = 75cm ≈ 29.5 inches
• 90 = 90cm ≈ 35.4 inches
• 120 = 120cm ≈ 47.2 inches

This is the single most useful thing to know, because length is usually what your shelf, cabinet or alcove constrains. Measure the space first, and the number picks itself.

Rule Two: The Letter Is the Profile

The letter tells you the proportions at that length — how deep front-to-back, and how tall.

C — Cube

Equal on all three sides. The 30C is 11.81 inches in every direction, 7.1 gallons. Cubes are excellent for a single dramatic piece of hardscape viewed from the front and both sides.

S — Shallow

Reduced height on a full footprint. The 60S is 23.62 × 14.17 × 7.09 inches. The shallow water column means light reaches the substrate easily, which is why these are so popular for carpets and for emersed-style layouts where hardscape breaks the surface.

L — Long and Slim

Narrow front-to-back with a roughly square cross-section. The 60L is 23.62 × 7.87 × 7.87 inches and only 6 gallons — a shelf tank in the truest sense. The 90L stretches the same idea to 35.43 × 11.81 × 11.81 and 21 gallons.

U — The Full-Depth Standard

The deepest and tallest body at any given length. The 60U is 23.62 × 14.17 × 14.17 inches, 20 gallons — the same footprint as the 60S with double the height. This is the default choice at 60cm and the one most people should start with.

P — Aquascaping Proportion

Sits one step below U in depth, with proportions tuned for composition rather than maximum volume. The 75P is 29.52 × 17.72 × 17.72 (36 gallons) and the 90P is 35.43 × 17.72 × 17.71 (44 gallons). The P sizes are the classic contest-scape shapes.

T — Tall

Extra height on a smaller footprint. The 60T is the 60U footprint with the height pushed to 17.72 inches, giving 24.3 gallons. The 30T is a 30C footprint at 17.72 inches tall. Good for tall stems and for layouts you want to read as a cliff or a canyon.

N, B and TM

N marks the small nano bodies (3N, 5N). B appears on the 90B, a 12-gallon long-format tank. TM is the Prism series — the 30TM at 9.7 gallons and the 25TM at 5.9 — a separate range with its own edge treatment rather than a variant of the standard tanks.

The Sizes, Side by Side

Choosing by the Space You Have

Work in this order and you will not get it wrong.

1. Measure length first. That picks your number. Leave at least a couple of inches of clearance either side for cleaning and for cable runs.
2. Then check depth front-to-back. This is the dimension people forget. A 60U needs 14 inches of usable surface depth; a standard 12-inch bookshelf will not take one.
3. Then decide height. Height is where the S, U and T variants split. Taller means more water volume and more stability, but also more light demand to reach the substrate and a harder reach for planting.

One thing worth saying plainly: bigger is easier. A 20-gallon 60U is far more forgiving of a dosing mistake or a missed water change than a 5-gallon 45S, because the same error is diluted across four times the water. If you are choosing between a nano and a mid-size and have the room, take the mid-size.

Choosing by What You Want to Grow

• Carpets — HC Cuba, Monte Carlo, dwarf hairgrass. Go shallow. A 60S or 75S puts the light close to the substrate, which is exactly what carpeting plants need. Carpets in a tall tank need considerably more light to succeed.
• Tall stem plants and a Dutch-style background. Go tall. A 60T or 45T gives you the vertical room to grow stems out and trim them back without the tank looking cramped within a fortnight.
• Iwagumi. Length and width matter more than height. Something like a 75S or 90P gives you the horizontal canvas to arrange stones with real negative space.
• Epiphytes — Bucephalandra, Anubias, ferns on wood. These are the least fussy about tank shape. Choose by where the tank is going, not by the plants.
• Shrimp only. A 30C or 45S is plenty, and the smaller volume makes a dedicated shrimp tank easy to keep stable if you are disciplined about feeding.

You can browse the full range in the tanks collection.

Rimless Tanks Need a Level, Fully Supported Stand

This is not optional and it is the most common expensive mistake in the hobby.

A rimmed aquarium has a plastic frame that ties the panels together and spreads load. A rimless tank has none of that. The silicone seams at the mitred corners carry the entire structural job, and they are designed on the assumption that the base panel is supported evenly across its whole area.

• The stand must be flat and level in both directions. A twist of even a couple of millimetres across a 90cm tank concentrates stress at one corner seam.
• The entire base must be supported. No overhang, no resting on a frame with a hollow middle, no sitting across two surfaces.
• Use the levelling mat. UNS tanks include a black mat for exactly this reason — it absorbs the small irregularities every surface has. Do not skip it, and do not substitute a towel.
• Check the load. Water is about 8.3 pounds per gallon before substrate and hardscape. A 44-gallon 90P full is comfortably over 450 pounds. Most domestic furniture is not built for that.

A purpose-built stand is sized to the tank footprint and has adjustable levelling feet, which solves all of the above at once. If you are using existing furniture, put a spirit level on it first and check it again once the tank is full — floors settle.

Frequently Asked Questions

What is the best first UNS tank?

The 60U for most people. Twenty gallons is forgiving, the 60cm footprint fits a standard cabinet, lighting and filtration for that size are widely available, and it is large enough for a real composition with foreground, midground and background.

Why is a 60S only 10 gallons when a 60U is 20?

They share the same 23.62 × 14.17 inch footprint. The 60S is 7.09 inches tall and the 60U is 14.17 — double the height, double the volume. Same shelf space, very different tank.

Do I need low-iron glass?

You do not need it, but you will notice it. Standard float glass has a green cast that gets stronger with thickness and is most obvious at the corners and when viewing at an angle. Low-iron glass removes that, which matters when you are looking at the tank every day.

Can I put a rimless tank on a normal chest of drawers?

Only if it is genuinely flat, genuinely level and rated for the weight — and most are not. Check the top for bow across the middle, which is common on flat-pack furniture. If it bows even slightly, the tank base is unsupported in the centre and loaded at the edges.