That's a great and practical question! Figuring out the right amount of soil is key to a successful planting project and avoids waste. For our standard medium-sized urban planter box, which typically measures approximately 24 inches long, 12 inches wide, and 12 inches deep (or 60cm L x 30cm W x 30cm D), the calculation is straightforward.
You simply multiply the Length x Width x Height to find the volume. Using the imperial measurements: 24" x 12" x 12" = 3,456 cubic inches. To convert this to cubic feet (the standard unit bagged soil is sold in), divide by 1,728 (the number of cubic inches in a cubic foot). So, 3,456 ÷ 1,728 = 2 cubic feet.
Therefore, you will need 2 cubic feet of potting soil to fill one medium-sized planter box to the brim. We always recommend using a high-quality potting mix for containers, not regular garden soil, as it provides better drainage and aeration for healthy roots. Most bags of potting mix are sold in quantities like 1 cubic foot or 2 cubic feet, so one 2-cu-ft bag would be perfect. Remember, if you're adding a drainage layer of stones at the bottom, you'll require slightly less soil. Happy planting