Pots & Containers Calculators

Container gardening is the ideal solution for millions of UK gardeners working with limited space — from balconies and courtyards to small terraced house gardens. Getting the right pot size and compost volume is essential for healthy plant growth, and our pot volume calculator handles round, square, and tapered containers in litres and cubic centimetres. The container compost calculator then works out exactly how many litres of multipurpose or peat-free compost you need to fill your pots, saving you from buying too many bags at the garden centre.

Window boxes and hanging baskets are a beloved part of British streetscapes, brightening up homes from spring through autumn. Our window box calculator works out compost volume and how many bedding plants to include based on your box dimensions, while the hanging basket calculator covers the 12-inch (30cm) and 14-inch (35cm) baskets most commonly sold in the UK. Grow bags remain one of the most popular ways to grow tomatoes, peppers, and courgettes in the UK — the grow bag calculator helps you plan how many standard 35-litre or 40-litre bags you need for your crop.

Proper drainage is critical for container plants, especially through the wet British winter when waterlogged compost causes root rot. The drainage layer calculator works out how many crocks or how much gravel to place at the base of larger pots, typically filling the bottom 2-5cm. As plants grow, the repotting size calculator advises stepping up by one pot size at a time (roughly 2-5cm larger in diameter), which avoids the common mistake of overpotting into a container that holds too much wet compost around small roots.