Bonsai Pot Size Calculator
30.5 × 21.5 × 5.5 cm
Oval · Informal Upright
What water does in that pot
With Akadama mix, roughly 2cm of water stays put at the bottom of any pot once it stops draining. In a 5.5cm pot that is 36% of the depth.
That is a normal trade-off for a display pot, not a problem. If you want more air at the roots, about 6.5cm of depth or a coarser substrate would get you there.
Where these numbers come from
The proportions are classical Japanese display convention: pot length around two thirds of the tree height, depth matching the trunk diameter just above the roots, round pots about a third of the height across.
Cascades break that on purpose, since the pot has to be tall enough to balance a trunk that falls below its own rim. Literati go the other way, a small shallow pot under a thin elegant trunk. When a tree is wider than it is tall, the canopy is what the pot has to carry visually, so the calculation switches to spread.
Why depth is a health decision, not just a look
Drainage stops when capillary attraction balances gravity, which leaves a saturated layer at the bottom of the container. Its height comes from the particle size of your substrate, not from how deep the pot is: the same mix leaves the same couple of centimetres of dead water in a 4cm pot and in a 20cm one.
That is why a shallow display pot filled with fine organic soil drowns roots while the same pot with sifted aggregate does not. If this calculator says a pot stays too wet, coarser substrate fixes it just as well as more depth.
How precise is this?
Not very, and it should not pretend to be. Two experienced growers will disagree by ten percent on the same tree and both be right. Use these numbers to narrow down which pots to shop for, then trust your eye on the final choice.
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