Short answer
Measure the surface first. Most toilet tank lids are about 17 to 20 inches wide and 7 to 9 inches deep, so a tank tray should be shorter than the lid and no deeper. On a vanity, a tray about half to two thirds of the clear counter leaves room to breathe. A bathtub tray must expand to your rim to rim width.
Tray size calculator
The size chart
Bathroom tray sizes at a glance
| Surface | Typical size | What to know | Source |
|---|---|---|---|
| Toilet tank lid | About 17 to 20 in wide, 7 to 9 in deep | Measure your lid upside down at its widest points; lids vary in small steps. | Frank Webb |
| Toilet tank, side to side | Rarely over 20 in; most 18 in or less | Small tanks can be about 15 in. A tray should be shorter than the lid it sits on. | Hunker |
| Vanity tray | Half to two thirds of the clear counter | Our styling rule of thumb, not a standard: it leaves a few inches open on each side. | Styling guide |
| Slim amenity tray | Example: 11-1/2 x 3 in | Umbra lists its Junip chrome amenity tray at this size: long and narrow for a sink ledge. | Listing |
| Bathtub caddy tray | Range must include your tub width | Measure across the tub from outer rim to outer rim, then check the listed minimum and maximum. | Bathtub trays |
| Shower tray (UK term) | Smallest common size 700 x 700 mm | A shower tray is a shower base, not a decor tray. UK sizes are listed in millimeters. | Bathroom Mountain |
How to measure without guessing
- Tank lid: lift it off, flip it, and measure the widest point side to side and front to back (Frank Webb). Note whether the top is flat or curved; a curved lid needs a tray with feet or a flat base that will not rock.
- Vanity: measure the clear stretch of counter where the tray will sit, from the sink edge to the wall or the end of the counter, and the depth from the backsplash to the sink rim.
- Tub: measure across the tub from outer rim to outer rim, straight across where you will sit.
- Your things: stand the items you want on the tray together and measure their footprint. Add about an inch all round so the rim does not crowd them.
Shape and depth
- Rectangular trays fit tank lids and narrow ledges best, because they use the full depth.
- Round and oval trays soften a square vanity and suit a corner, but waste space on a narrow ledge.
- Rim height: a low rim (about half an inch) shows off bottles; a deeper rim keeps rolling things like cotton rounds and lip balm in place.
- Tiered trays double the space on a small counter, but put the heavy things on the bottom tier.
Not sure which style? Try the tray finder or read the toilet tank tray guide.
Questions people ask
What size tray fits on a toilet tank?
One shorter than your lid and no deeper than it. Most lids are about 17 to 20 inches wide and 7 to 9 inches deep, so trays around 12 to 16 inches long and up to about 7 inches deep suit many tanks. Measure yours: lids vary.
How big should a vanity tray be?
There is no rule, but a tray about half to two thirds of the clear counter beside the sink leaves a few inches open on each side, which usually looks intentional rather than crowded. It is a styling rule of thumb, not a standard.
How do I measure a bathtub for a caddy tray?
Measure straight across the tub from the outer edge of one rim to the outer edge of the other. Expandable caddies list a minimum and maximum length; your number should sit inside that range so the arms rest fully on both rims.
How do I measure a toilet tank lid?
Lift the lid off, turn it upside down, and measure the widest point left to right and front to back. Frank Webb, a plumbing parts retailer, recommends exactly this because lids vary in small increments.
Sources
Last reviewed October 12, 2026. Sizes, finishes and listings change; check the product details and measurements before you buy, and follow the maker’s care instructions.