Soil Amendment Calculator

It multiplies the area by the depth after converting the depth from inches to feet, so volume in cubic feet equals area in square feet times depth divided by 12. A 100 square foot bed at 2 inches deep is 100 times 2 divided by 12, which is 16.6667 cubic feet.

Area is in square feet, depth is in inches and bag size is in cubic feet. Results come back as cubic feet, cubic yards and a whole bag count, so you can order in whichever way your supplier sells.

There are 27 cubic feet in a cubic yard. Bulk compost and topsoil are usually sold by the cubic yard, so the tool divides your cubic feet by 27 to give the bulk figure for a truck or trailer order.

Amendment is sold by the whole bag, so any partial bag rounds up to the next one. The 100 square foot example needs 8.33 bags of 2 cubic feet, which rounds up to 9. A little extra is handy for topping off thin spots.

Yes. Set the Bag size field to 0 and the Bags card reads n/a, leaving just the cubic feet and cubic yards for a bulk delivery. Any positive bag size, such as 1, 1.5 or 2 cubic feet, switches the count back on.

A quarter to a half inch suits an annual lawn top dressing, which is why the tool notes that range. Garden beds can take one to three inches of compost worked into the surface before planting.

Volumes are rounded to four decimal places and bags to a whole number. The estimate is only as good as your measurements, so measure the area carefully, and firming or settling the material can change how far a bag actually goes.

Compost improves structure and feeds soil life, so it suits most beds. Aged manure adds nutrients and topsoil adds bulk. Many gardeners blend compost with topsoil, and the volume math is the same whichever you choose.

Yes. The calculation runs entirely in your browser, so your measurements never leave your device and nothing is uploaded to a server.