Fill the bed, not the truck twice

Getting the fill right

The core math

Length × width × depth, all in feet, gives cubic feet; divide by 27 for cubic yards. The only common mistake is forgetting to convert depth from inches to feet — a 4×8 bed at 10 inches is 4 × 8 × 0.83 ≈ 26.7 cubic feet, almost exactly one yard.

Why add a settling allowance?

Fresh soil, especially fluffy bagged mixes and anything high in compost, compacts noticeably in the first weeks of watering. Filling to the brim on day one leaves you a couple of inches low by month two. Ten percent extra is a sensible default for new fills.

How deep should the soil be?

Six inches grows lettuce and herbs; ten to twelve inches suits most vegetables including tomatoes and peppers; root crops like carrots and daikon appreciate twelve or more. If your bed sits on open ground, roots can continue into the native soil below, so a shallower fill still works better than the same depth on a hard surface.

Bags or bulk?

Bags win on convenience and small quantities. By volume they're expensive: a yard of bulk garden mix commonly costs what a dozen bags do while containing eighteen 1.5 cu ft bags' worth of soil. The calculator flags when you cross into bulk territory.