Compost Calculator
Topdressing 1,000 square feet at 1/2 inch takes 41.67 cubic feet, 1.54 cubic yards, and 42 bags of 1 cubic foot. Nothing is turned into the lawn.
Last updated . Topdress is the opening job. Area starts at 1,000 ft² and depth at 0.5 in. The bag menu starts at 1 cubic foot. No price.
A compost calculator with two jobs. A lawn topdress is only the compost you spread. Mixing into a bed also reports the incorporation volume, the soil you turn, and the compost’s share of that turned layer.
Bulk soil, not compost: topsoil calculator. A yard of surface cover: mulch calculator. Seed on the dressed lawn: grass seed calculator.
Compost for a lawn or a bed
Topdress depth opens at 1/2 inch. The bed layer opens at 3 inches and the mix depth at 8 inches, the low ends of the ranges in Oregon State EM 9308. Bag size opens at 1 cubic foot. The 2 cubic foot choice is the other bag size that bulletin names.
Results
Topdress volume versus the soil you turn
Cubic feet are the area times the depth in feet. Inches are divided by 12 before that multiply. Yards are those cubic feet divided by 27. Bags round the cubic feet up to the bag size you pick: 1 cubic foot, 2 cubic feet, or a size you type. A topdress stops there. Mixed layer reads Surface only, and the share is a dash, because the compost stays on the grass.
A bed is two volumes. Compost is the area times the layer you haul in. Mixed layer is the area times the depth you turn, which is the incorporation volume. Share is the layer depth divided by that mix depth. The mix has to be deeper than the layer, or the form stops and explains why. The opening bed is 3 inches of compost turned through 8 inches, so the share is 37.50 percent and the turned soil is larger than the compost order.
Depths follow Oregon State University Extension publication EM 9308, “How to use compost in gardens and landscapes,” by Weston Miller and Jeremiah Mann (February 2021, reviewed 2025): a lawn dressing of one-quarter inch to one-half inch, and a new bed layer of 3 to 4 inches incorporated into the top 8 to 12 inches. The form opens at the thick lawn dressing and at the shallow end of that bed pair. The source is extension.oregonstate.edu/pub/em-9308. This page is not a topsoil takeoff and not a mulch takeoff.
Volumes for the two jobs
| Case | Compost | Yards | Bags | Mixed layer |
|---|---|---|---|---|
| 1,000 ft² topdress, 1/2 in, 1 cu ft bags | 41.67 ft³ | 1.54 yd³ | 42 | Surface only |
| Same topdress, 2 cu ft bags | 41.67 ft³ | 1.54 yd³ | 21 | Surface only |
| 100 ft² bed, 3 in into 8 in, 1 cu ft bags | 25.00 ft³ | 0.93 yd³ | 25 | 66.67 ft³ |
Worked example
Leave Topdress a lawn, 1000 ft², 0.5 in, and 1 cu ft. Compost reads 41.67 ft³ · 1.18 m³. Cubic yards reads 1.54 yd³. Bags reads 42. The arithmetic is 1,000 × 0.5 ÷ 12 = 41.666… cubic feet, then ÷ 27 = 1.543… yards. Bags round 41.666… up to 42.
Compost questions
How much compost topdresses 1,000 square feet at 1/2 inch?
Leave Job on Topdress a lawn, area 1000 ft², depth 0.5 in, and bag size 1 cu ft. Compost reads 41.67 ft³ · 1.18 m³. Cubic yards reads 1.54 yd³. Bags reads 42. Mixed layer reads Surface only. Compost share reads —.
How many bags if each bag is 2 cubic feet?
Leave the 1,000 ft² topdress at 0.5 in and set Bag size to 2 cu ft. Compost stays 41.67 ft³ · 1.18 m³ and Cubic yards stays 1.54 yd³. Bags reads 21. The volume is 41.666… cubic feet, and 41.666… ÷ 2 rounds up to 21.
What is the incorporation volume for a 100 square foot bed?
Set Job to Mix into a bed, area to 100 ft², compost layer to 3 in, mix depth to 8 in, and bag size to 1 cu ft. Compost reads 25.00 ft³ · 0.71 m³. Cubic yards reads 0.93 yd³. Bags reads 25. Mixed layer reads 66.67 ft³ · 2.47 yd³. Compost share reads 37.50%.
Why is the share 37.50 percent?
The compost product is the 3 inch layer: 100 × 3 ÷ 12 = 25 cubic feet. The incorporation volume is the soil you turn, 100 × 8 ÷ 12 = 66.666… cubic feet. Share is 3 ÷ 8 = 37.50%. The mixed-layer line is that turned soil, not a second order of compost.
Where do the opening depths come from?
Oregon State University Extension EM 9308, Weston Miller and Jeremiah Mann, published February 2021 and reviewed in 2025, says an existing lawn is dressed one-quarter to one-half inch deep, and a new garden bed gets a 3 to 4 inch layer worked into the top 8 to 12 inches. This form opens on 1/2 inch, and on 3 inches worked into 8 inches. The same bulletin’s check figures are exact here: 1 cubic foot covers 12 square feet at 1 inch, and a 2 by 2 foot patch at 3 inches is 1 cubic foot. Purchased bags in that bulletin are often 1 or 2 cubic feet, which is why those two sizes are on the menu.
Is this the topsoil yard or the mulch yard?
No. Bulk soil by the yard is the topsoil calculator. A surface mulch yard is the mulch calculator. This page is only the compost layer, either left on a lawn or turned into a bed. It does not apply a soil density, and it does not price a bag.
What if the mix is not deeper than the layer?
Set the mix depth equal to the compost layer, or shallower. The note reads: The mix depth is not deeper than the compost layer, so the layer is not turned into a thicker bed. A blank area reads: Enter an area greater than zero. A blank topdress reads: Enter a topdress depth greater than zero. A blank bed layer reads: Enter a compost layer and a mix depth, each greater than zero. A blank custom bag reads: Enter a bag size greater than zero.