How much soil does a large, rectangular planter box typically hold?

I stretch my wooden sides under the warm sun, feeling the eager roots of tomatoes and basil tickling my empty belly. “How much soil do I need?” you whisper, tape measure in hand. I hear you. So let’s get to the dirt of it.

I am a large rectangular planter box—say, 6 feet long, 2 feet wide, and 1.5 feet deep. That’s 72 inches long, 24 inches wide, and 18 inches deep for the metric-curious. To fill me properly, you need to calculate my volume: length × width × depth. In this case, 6 × 2 × 1.5 equals 18 cubic feet. Yes, 18 bags of that 1-cubic-foot potting mix you buy at the garden center. I am a hungry beast!

But I have a secret: I don’t need to be filled to the brim. Leave about an inch of empty space at the top (0.08 feet) so water doesn’t overflow and soil doesn’t wash away when you water me. So really, I need about 6 × 2 × 1.42 = 17.04 cubic feet. Round it up to 18 bags—you’ll use the leftover for my companion pots.

If I’m larger—say 8 feet by 3 feet by 2 feet deep—I hold 48 cubic feet. That’s a truckload! Small boxes (2×1×1 feet) hold just 2 cubic feet. See the pattern? Measure me, multiply my three dimensions, and you’ll never leave me half-empty again. I promise to hug your roots tightly if you do.

So, grab your calculator. I’m ready to be filled with rich, dark soil. And please, pat me gently when you’re done—it feels like a hug.