Container Garden Volume Calculator

Container Shape changes Total Soil Volume the most for a like-for-like swap: switching between Round, Square, and Rectangular at the same diameter/length and depth moves the total noticeably, because the three shapes use genuinely different formulas rather than a shared one with a shape-specific multiplier. Round pots use pi times radius squared times depth; square containers use side squared times depth; rectangular ones assume the width is 60% of the entered length and multiply length by that assumed width by depth — at the same diameter and depth, that assumed 60%-width rectangle holds noticeably less soil than a round pot, which in turn holds less than a square one. But over the full range of values you could enter, Container Diameter/Length is the real heavyweight: because it enters every shape's formula squared, and its own allowed range spans 4 to 60 inches (a 15x span), a container at the top of that range can hold vastly more soil than one at the bottom — far beyond what swapping shapes at a fixed size can produce. Container Depth and Number of Containers, by contrast, only enter linearly, so doubling either one only roughly doubles the volume, not quadruples it the way doubling Container Diameter/Length does.

Volume per Container is converted from cubic inches to US gallons at 231 cubic inches per gallon, then multiplied by Number of Containers for Total Soil Volume. Soil Bags Needed rounds that total up to whole 1-cubic-foot bags (7.48 gallons each), so it only increases in discrete steps rather than smoothly with every small volume change. Total Weight (wet) assumes a flat 7 lbs per gallon for moist potting mix — real bagged mixes vary roughly 6-8 lbs per gallon depending on composition and moisture — and Estimated Soil Cost assumes a flat $8 per bag, which will differ from your local retail price. The rectangular-shape width assumption (60% of length) is this calculator's own simplification for containers where you only enter one length dimension; it won't match an unusually long, narrow, or wide rectangular planter exactly.