Container Size Chart
Container size decides how much root space, water, and nutrients a plant gets, and the most common balcony gardening failure is a pot too small for the crop. This chart matches pot sizes to plants, converts between the gallon, litre and inch labels suppliers use, and covers the weight question that matters specifically on a balcony.
Pot size conversions
1 gallon = 3.8 litres, roughly 6-7 inch / 15-18cm diameter pot.
2 gallon = 7.6 litres, roughly 8-9 inch / 20-23cm.
3 gallon = 11.4 litres, roughly 10 inch / 25cm.
5 gallon = 19 litres, roughly 12 inch / 30cm. The classic bucket size.
7 gallon = 26.5 litres, roughly 14 inch / 35cm.
10 gallon = 38 litres, roughly 16-17 inch / 40-43cm.
15 gallon = 57 litres, roughly 18-20 inch / 45-50cm.
Minimum container size by crop
Herbs (basil, parsley, cilantro, chives): 1-2 gallon / 4-8 litres each, or a shared window box at 8 inches deep.
Lettuce and salad greens: 1-2 gallon, shallow rooting so depth matters less than surface area.
Radishes, spinach, bush beans: 2-3 gallon.
Peppers and eggplant: 5 gallon minimum, 7 gallon preferred for full-size plants.
Determinate (bush) tomatoes: 5-7 gallon. Indeterminate (vining) tomatoes: 10 gallon minimum, and they will still need staking and heavy feeding.
Cucumbers and summer squash: 5-7 gallon with a trellis.
Potatoes: 10-15 gallon, or a dedicated grow bag, since yield scales directly with soil volume.
Dwarf fruit trees and shrubs: 15 gallon and up, and expect to root-prune or pot up every few years.
Weight: the balcony-specific constraint
Wet potting mix weighs roughly 0.7-0.9 kg per litre. A 15 gallon (57 litre) container of saturated soil weighs around 40-50kg before the plant, the pot, or standing water is counted.
Balconies have structural load limits, usually specified per square metre, and clustering several large containers in one spot concentrates that load badly. Distribute heavy pots along the wall edge (where the structure is strongest) rather than at the outer railing, keep the largest containers to a minimum, and check your building's limits if you are planning anything substantial.
Fabric grow bags and plastic containers weigh a fraction of ceramic or concrete pots at the same volume, which is the easiest weight saving available.
Depth versus width
Root depth requirements differ by crop: lettuce and herbs are happy at 15-20cm deep, peppers and bush beans want 25-30cm, and tomatoes, potatoes and root vegetables need 40cm or more.
A wide shallow planter and a narrow deep pot can hold identical volume while suiting completely different plants, so check the depth specification rather than only the litre or gallon figure when matching a container to a crop.