Soil Calculator
Yards or bags of soil for any bed, plot, or planter
What is soil calculator?
A soil calculator answers the gardener’s first question on any new bed: how many bags or cubic yards do I need to fill it. The volume math (length times width times depth) is straightforward; the wrinkle is that bagged soil at retailers comes in inconsistent sizes (1, 1.5, or 2 cu ft) and bulk landscape soil is priced by the cubic yard.
The default density is 80 lb/ft³ for screened garden soil at moderate moisture. Bagged “garden soil” with peat and compost amendments is a bit lighter (60-70 lb/ft³); heavy clay topsoil is closer to 100 lb/ft³. Volume math doesn’t change; only the weight readout differs.
What depth to choose? Six inches is the minimum for shallow-rooted greens, herbs, and most flower bed annuals. Twelve inches works for the majority of vegetables. Eighteen inches is best for root crops (carrots, parsnips, beets) and any deep-rooted perennial like asparagus or rhubarb. For lawn top-dressing or overseeding, a quarter to half inch is plenty — anything more and you smother the existing grass.
Bulk vs bagged: at landscape supply yards, bulk garden soil typically runs ~$30-50 per cubic yard delivered. A cubic yard equals about 27 of 1-cu-ft bags or 18 of 1.5-cu-ft bags. By the time you’re past 1.5 yards (35-40 bags), bulk wins on price and saves the lifting. Below that, bags are easier — and you can stage the buying over multiple weekend trips.
The 10% waste factor default covers spillage during transfer from bag or wheelbarrow to bed, and minor spread loss at the edges. For raised beds, bump to 15% so you have extra to top off after the inevitable first-month settle. Soil compacts about 10-15% in the first few weeks of watering — fresh-filled beds always look a little under-filled by mid-season.
When to use a soil calculator
- New garden bed prep — Filling a 4 ft x 8 ft raised bed with garden soil. The calculator outputs both yards and bag count for easy comparison shopping.
- Lawn renovation top-dress — 1/4 to 1/2 inch of soil over a thin lawn for overseeding. Even a small lawn needs more soil than the depth suggests.
- Container and planter fill — Big planters and patio pots eat soil quickly. Enter average diameter and depth (or rectangular dimensions) for the order quantity.
How to use the Soil Calculator
- Measure the area — For raised beds, multiply length by width. For round planters, the calculator takes diameter directly. For irregular plots, break the area into rectangles and add results.
- Pick a depth — Use 6 inches minimum for vegetable beds (12 inches for root crops), 1/4-1/2 inch for top-dressing a lawn, and the full container depth for planters.
- Read the bag count — Output shows bags of the size you selected. Bagged garden soil typically comes in 1-cu-ft or 1.5-cu-ft sizes. Round up — partial bags don't store well outdoors.
- Apply waste factor — 10% covers spillage during transfer and minor spread loss. Bump to 15% for raised beds where you may want extra to top off after settling.
Worked examples
4 ft x 8 ft raised bed at 12 in
Input: 4 ft x 8 ft x 12 in depth
Output: 1.30 cu yd / 35.2 cu ft / 2,816 lb (with 10% waste)100 ft^2 lawn top-dress
Input: 10 ft x 10 ft x 0.5 in depth
Output: 0.17 cu yd / 4.6 cu ft / 367 lbTop-dressing screened soil is finer and spreads further than bagged garden soil.
Round planter, 4 ft diameter at 18 in
Input: Circle 4 ft diameter x 18 in depth
Output: 0.69 cu yd / 18.7 cu ft / 1,492 lb