Figuring out how much soil you need for your new urban planter boxes is simpler than you might think. The key is calculating volume using a basic mathematical formula. Start by measuring your planter box's interior dimensions in feet: length, width, and depth. Multiply these three numbers together (length × width × depth) to find the volume in cubic feet.
For example, a planter that's 4 feet long, 2 feet wide, and 1.5 feet deep would require 12 cubic feet of soil (4 × 2 × 1.5 = 12). Most bagged soil is sold in cubic feet measurements, typically 1-2 cubic feet per bag, making it easy to determine how many bags you need.
Remember to account for settling and compression by adding about 10-15% extra to your total calculation. This ensures you have enough soil to properly fill your planter after it settles. For irregularly shaped planters, break them down into rectangular sections and calculate each separately before adding them together.
Always use high-quality potting mix rather than garden soil, as it provides better drainage and aeration for container plants. With these simple calculations, you can confidently purchase the perfect amount of soil for your urban gardening project without waste or multiple trips to the garden center.