Choose a pot size and calculate your growing medium volume
Litres and outer dimensions answer different questions. Choose a pot for your plant and setup, then make a useful estimate of the soil or coco you need.
Start with the plant and available space
Choose pot capacity for the plant species, stage, root ball and watering method. No general rule assigns one litre size to every young or mature plant. A large pot is not automatically the best start for a small root ball.
Measure where the pot will stand. Include width, height, saucers and space for moving plants. In a tent, allow free space above the plant too. Explore Plant pots and check the exact model’s dimensions.
Compare litres with centimetres
The square 14 litre pot measures 28 × 28 × 28.5 cm. The 18 litre pot measures 31 × 31 × 31.6 cm; the 25 litre pot measures 33 × 33 × 35 cm. Outer dimensions determine practical fit, while litres describe nominal capacity.
Do not multiply outer dimensions to calculate filling volume. Pots can taper and have walls, bases and a watering rim. Use stated litres for the first estimate and centimetres for planning the setup.
Add up the nominal capacity
Number of pots × capacity per pot = nominal total. Four 14 litre pots give 4 × 14 = 56 litres. Two 18 litre pots and two 14 litre pots give 2 × 18 + 2 × 14 = 64 litres. These are calculation examples, not recommended plant counts.
Compare that total with bag capacity. A 50 litre bag is nominally less than 56 litres. Whether you actually need more also depends on space at the rim and existing root balls. Account for those conditions instead of expecting an exact number of filled pots per bag.
Check the actual filling requirement
When repotting, the existing root ball already takes up space. You mainly fill around it and leave watering space at the top. Where possible, make a trial filling and record the medium used.
Do not compact a loose medium hard to fit more litres in the pot. Roots need air too. Check the use instructions for Grow soil for indoor growing and Coco coir. Our soil or coco guide helps you choose between them.
Include watering and drainage
A different pot size changes the relationship between roots and moist medium. Check watering and drainage after repotting instead of automatically keeping the old routine. Measure nutrient solution with a suitable Measuring jugs.
Starting young plants? Explore Propagation supplies and our plug and starter block guide before choosing a large final pot. Via Growing media & pots, you can also find trays, saucers and accessories for your layout.