Pot Size & Potting Mix Calculator
Get the right next pot size when repotting and how much potting mix you'll need to fill it.
For reference, your current 6" pot holds roughly 1.9 qt (2.1 L) of mix. These are estimates: mix settles over time and the root ball itself takes up space, so buy a little extra.
How it works
Enter the diameter of the pot your plant is in right now, and the calculator suggests the next size up: 2 inches for anything 10 inches or smaller, 4 inches for anything bigger. Small jumps keep a small plant from sitting in too much wet soil it can't use yet. Larger plants can handle (and need) a bigger jump to make repotting worth doing.
It also estimates how much potting mix fills that new pot. The math treats the pot as a cylinder that tapers slightly toward the bottom, so a 6 inch pot needs about 1.9 quarts of mix and an 8 inch pot needs about 4.5 quarts. Worked example: your plant is in a 6 inch pot, so the calculator recommends an 8 inch pot and about 4.5 quarts (4.3 liters) of fresh mix to fill it. That number is an estimate. Mix settles as you water it in, and the root ball itself displaces some volume, so grab a little extra rather than running short halfway through.
FAQ
Do I always need to size up when repotting?
Not always. If a plant just needs fresh soil (the old mix has broken down or gone stale) you can repot into the same size pot. Size up specifically when roots are circling the bottom, growing out the drainage holes, or the plant dries out within a day or two of watering.
Why not jump straight to a much bigger pot?
Too much extra soil around a small root system holds water the roots can't take up fast enough, which is a common cause of root rot. The small, steady jump this calculator recommends keeps the plant growing into soil it can actually use.
Does the potting mix estimate account for drainage material?
No, it's the volume of mix alone. If you like to add a layer of pebbles or extra perlite at the bottom for drainage, buy a bit more mix than the number shown here.
What if my pot is a weird shape, not a standard round nursery pot?
The estimate assumes a fairly standard pot where the height is close to the diameter. Shallow bowls or tall cylinder planters will need less or more mix than shown, so treat the number as a starting point and have a little extra mix on hand either way.
For more on choosing pots and getting the repot itself right, see how to choose the right pot for your plant, how to repot a houseplant without killing it, and the best soil for houseplants, explained.