Topsoil Calculator

How to use the topsoil calculator

Measure the area in feet — length times width — and split irregular spaces into rough rectangles, adding the results together. For a curved bed, use the average width. Lawn areas are usually the big number here, so pace them off or pull the dimensions from a property plat rather than eyeballing: being 20% off on a lawn-sized area is a wheelbarrow-hour of difference.

Depth is where topsoil differs from mulch math. A brand-new planting bed or a lawn started from bare grade wants 4–6 inches of quality topsoil — grass roots live in that band. Topdressing an existing lawn to smooth low spots or feed thin turf takes only half an inch to one inch; more than that smothers the grass underneath. Raised-bed fills and badly eroded spots can run the slider to 8 inches, calculated per layer if you’re mixing in compost.

Know what you’re buying, because the words matter at the supply yard. Topsoil is screened earth with organic content — the planting layer. Fill dirt is subsoil: cheap, structureless, fine under a slab or for grading, wrong for anything you want to grow. Garden soil is topsoil pre-blended with compost and sold at a premium, sensible for raised beds and small gardens but wasteful to spread by the yard. This calculator’s number works for any of them; the label decides what to pour.

The result reads two ways. Cubic yards is the bulk-delivery number — what a dump truck quote uses. The bag count converts the same volume into store bags, defaulting to the common 0.75 cu ft bag (switch sizes under Advanced). Topsoil bags are small and heavy — around 40 lb each — so the bag count climbs shockingly fast: even a modest bed turns into dozens of bags.

That’s why bulk wins earlier with topsoil than with most materials. Past roughly half a cubic yard — about 18 standard bags — a bulk delivery or a pickup-truck load from the landscape yard is cheaper and far easier on your back. Reserve bags for patch jobs, container mixes, and topping a single low spot.

The formula

Straight volume math: area times depth, inches converted to feet, then cubic feet to the yards bulk soil is sold in:

cubic feet = length × width × (depth ÷ 12)
cubic yards = cubic feet ÷ 27
bags = cubic feet ÷ bag size, rounded UP to a whole bag

Worked example with the defaults: a 10 × 10 ft area at 4 inches deep is 10 × 10 × (4 ÷ 12) = 33.3 cubic feet — 1.23 cubic yards. In standard 0.75 cu ft bags that’s 33.3 ÷ 0.75 = 44.4, so 45 bags. One number, two very different shopping trips.

Useful anchors: a cubic yard of topsoil covers about 108 sq ft at 3 inches (or roughly 325 sq ft at 1 inch) and weighs roughly a ton when dry — more after rain. Order on the yard number and let the supplier’s truck do the lifting.

Frequently asked questions