Which depth should I use — topdressing, existing bed, amendment, or new bed?

It depends on the job. Lawn topdressing worked into turf is about ¼" (Penn State Extension). An existing bed's annual maintenance dose is ¼-1", defaulting to ½" (OSU EM 9308). A soil-amendment pass is 1-2", tilled into the top 4-6" (Penn State). A new bed being established from bare ground gets 3-4", incorporated into the top 8-12" (OSU EM 9308). These are four different jobs, not a disagreement between sources.

What happens if I apply too much compost at once?

Past UNH Extension's general ceiling of about 4 cubic yards per 1,000 sq ft, Oregon State University Extension's guidance notes that soluble salt levels in the root zone can rise enough to injure plants, with seedlings and transplants most susceptible. This calculator flags the ceiling automatically as a soft caution, not a hard stop — a single heavy pass on an established bed is different from broadcasting the same rate around new seedlings.

Why does thick, un-worked-in topdressing hurt my lawn?

Penn State Extension's turf-performance guidance warns that successive thick topdressing layers left on the surface without incorporation build up a mat of organic matter that dries out turf roots and restricts rooting — the opposite of the intended benefit. Topdressing is meant to be thin and worked in, not stacked pass after pass.

How many bags of compost are in a cubic yard?

One cubic yard is 27 cubic feet, so that's 27 bags at 1 cu ft each, or 13.5 bags at 2 cu ft each. Bulk delivery is almost always cheaper than bagged past about a cubic yard, once packaging and handling costs are factored in.

Should I order based on the loose or settled depth?

Settled. Compost keeps breaking down and settling after it's applied, even more than topsoil does, since it's still actively decomposing. Order based on the depth you want after it settles, and let the waste factor cover the difference.

← Landscape Material Calculators

Compost Calculator

Compost is sold by the cubic yard, not the ton, so this calculator leads with volume and treats weight as a secondary figure — useful for delivery and truck-sizing, not the number to order by. Compost is also not topsoil, and ordering it like topsoil is the single most common mistake this calculator exists to head off: pound for pound, compost is far lighter and far bulkier than soil, since it's built from broken-down organic matter rather than mineral particles. Enter the length and width of your area, pick a depth — or tap a preset for lawn topdressing, an existing bed, a soil amendment pass, or a new bed, each tied to a specific university extension recommendation — and the results update as you type. Weight shows as a wide range rather than a single number, because compost's density swings more with moisture and screening than any other material on this site; see the guidance below for why, and for a soft caution if your entered area and depth add up to more compost than general application guidance recommends.

Your area

Shape

LengthWidthUnit

Depth

QuantityMultiplies the volume below — use this for multiple identical holes, footings, or beds instead of running the calculator once per unit.

Waste (%)Not sourced to any of the four extension citations on this page — none of them states an application-loss figure. 10% is a general handling allowance for spillage and uneven coverage while spreading, not a researched value. Lower it for careful hand-spreading on a small bed, where waste is minimal; raise it for a large area, an uneven surface, or wind.

Price (optional)

Enter your dimensions above to see results.

How it's calculated

The core conversion is one step: cubic yards = area (sq ft) × depth (in) ÷ 324 — the same math as every other material on this site (area × depth ÷ 12, then ÷ 27 for cubic yards), just collapsed into a single divisor since 12 × 27 = 324. A waste percentage is added on top (10% by default — a general handling allowance for spillage and uneven coverage while spreading, not a figure from any of the four extension sources below), and the adjusted cubic yardage is what this calculator treats as the primary result. Weight is computed from that adjusted volume using compost's density, but shown as a range (0.40-0.80 tons/yd³) rather than a point figure, since a specific batch's real density depends on moisture and screening in a way no calculator can know in advance. Bag counts divide the adjusted cubic feet by each bag's yield; truckloads divide the adjusted cubic yards by the truck's capacity.

Worked example

A 10 ft × 10 ft bed amended 2 inches deep (the soil-amendment preset): 100 sq ft × 2 in ÷ 324 = 0.62 yd³. Adding the 10% waste default: 0.62 × 1.10 = 0.68 yd³ — the amount to order. At 0.50 tons per cubic yard, that's 0.68 × 0.50 = 0.34 tons, or a 0.27-0.54 ton range across the full 0.40-0.80 density span — read as a delivery-weight estimate for truck sizing, not a precise order figure. In bags, the adjusted 18.3 cu ft (0.68 yd³ × 27) needs 19 bags at 1 cu ft, or 10 bags at 2 cu ft. This particular example also crosses UNH Extension's application-rate ceiling and would show this calculator's soft caution — not because 100 sq ft is a large area, but because 2 inches works out to about 6.17 cubic yards per 1,000 sq ft on its own (base volume, before waste), regardless of how much total area it's spread over. See the guidance below for why that ceiling is really a depth check in disguise.

How deep should it be?

This calculator leads with volume because that's how compost is actually sold and priced — by the cubic yard, not the ton — and treats the tons figure as a secondary number for delivery trucks and loader buckets, not a figure to order against. Weight is shown as a range rather than a single point specifically because compost's density is the least predictable figure on this site: Oregon State University Extension's EM 9217 states screened compost at 50% moisture runs about 1,000 lb per cubic yard but ranges 800 to more than 1,600 lb per cubic yard depending on moisture, particle size, and compaction, and UNH Extension separately notes no two batches are likely to be uniform even from the same supplier. A dry, coarsely screened load and a wet, finely screened load of the same visual volume can weigh nearly twice as much, one versus the other — order by volume, and treat the weight range purely as a planning number for how big a truck or how many loader passes a delivery will take. Each depth preset above ties to a specific recommendation rather than a rounded guess: lawn topdressing at ¼ inch worked into the turf comes from Penn State Extension's turf-performance guidance; an existing bed's annual maintenance dose runs ¼ to 1 inch (this page defaults to ½) per Oregon State University Extension's EM 9308 gardens-and-landscapes guide; a soil-amendment pass runs 1 to 2 inches (defaulting to 2), tilled into the top 4 to 6 inches, per Penn State's same guidance; and establishing a brand-new bed calls for 3 to 4 inches (defaulting to 3), incorporated into the top 8 to 12 inches, per OSU's EM 9308. Penn State's guidance carries a caution worth repeating directly: successive thick topdressing layers applied without working them in can build up a mat of surface organic matter that dries out turf roots and restricts rooting, rather than improving the lawn — a topdressing pass is meant to be thin and worked in, not stacked. Application rate matters at the other extreme too. UNH Extension's practical ceiling is about 4 cubic yards per 1,000 sq ft; past that, Oregon State University Extension's guidance on interpreting compost analyses notes that heavy application rates can raise soluble salt levels in the root zone enough to injure plants, with seedlings and transplants the most susceptible. This calculator flags that ceiling automatically if your entered area and depth would exceed it — a soft caution, not a hard stop, since a single heavy pass on an established bed is a different situation from broadcasting the same rate around new seedlings. Worth understanding directly: "cubic yards per 1,000 sq ft" is really a depth check wearing an area unit, since area cancels out of the ratio — using the base (pre-waste) volume, any depth past about 1.3 inches crosses UNH's ceiling regardless of how much total area it's spread over. That means the soil-amendment and new-bed presets above will routinely show this caution, on a small bed or a large one alike — expected, not a malfunction, and not a contradiction of OSU's own 1-2" and 3-4" depth guidance, which addresses what a job needs, not the separate salt-loading concern UNH's ceiling is about. Compost, topsoil, and garden soil blends get confused constantly, but they do different jobs: compost is fully broken-down organic matter, a soil amendment rather than a growing medium on its own, meant to improve structure, drainage, and nutrient content in soil that's already there; topsoil is mineral-based soil, used to build up grade or fill a bed from scratch; garden soil blends start with topsoil and mix in compost and other amendments, sold pre-mixed for planting beds. For bag math: one cubic yard is 27 cubic feet, so a cubic yard of compost is 27 bags at 1 cu ft each, or 13.5 bags at 2 cu ft each — arithmetic worth knowing before comparing a bagged unit price to a bulk delivery quote.

Common mistakes

Ordering compost by weight instead of volume. Compost is sold by the cubic yard, and its weight varies so much by moisture and screening (800 to over 1,600 lb per cubic yard) that a weight-based order can be significantly off from what a volume-based one would deliver.
Confusing compost with topsoil or a garden soil blend. Compost is an amendment for soil that's already there, not a standalone fill — building a new bed from bare ground needs topsoil or a blend as the bulk of the fill, with compost mixed in.
Applying a thick topdressing layer without working it in. Penn State Extension warns that successive unincorporated layers build up surface organic matter that dries turf roots and restricts rooting — topdressing should be thin (about ¼") and worked into the turf, not stacked.
Exceeding roughly 4 cubic yards per 1,000 sq ft in one application. Past UNH Extension's general ceiling, heavier rates can raise soluble salt levels enough to injure plants, especially seedlings and transplants — split a heavy application across passes or seasons instead.
Measuring the loose delivered depth instead of the settled depth. Compost keeps breaking down and settling after it's spread, more than topsoil does, so what you spread today isn't what remains in a few weeks.
Assuming a second bulk order will match the first exactly. Compost varies batch to batch, even from the same supplier, because the organic feedstocks going into it change over time.

Where the density figure comes from

This is the first density on this site sourced to university extension services rather than suppliers, and that's deliberate: extension services publish compost bulk density because farmers and land-grant researchers need it for application-rate math, so these figures are measured rather than estimated. UNH Extension states compost should generally run about 1,000 lb per cubic yard, give or take a few hundred pounds, and notes that no two batches are likely to be uniform, even from the same supplier. Oregon State University Extension's EM 9217 states screened compost at 50% moisture runs about 1,000 lb per cubic yard, with a full range of 800 to more than 1,600 lb per cubic yard depending on moisture, particle size, and compaction — the widest range on this site, because compost's weight depends on how wet, how finely screened, and how packed a given load is far more than any mineral material's does. 1,000 lb (0.50 tons) per cubic yard is the point figure this calculator uses to compute weight; the full 800-1,600 lb range (0.40-0.80 tons/yd³) is shown deliberately wide alongside it, because weight here is a secondary figure for delivery and truck-sizing — not a number to order by. See the guidance below for why this page leads with volume instead. We use 0.5 tons/yd³ as the display figure, drawn from:

FAQ

Why does this calculator show weight as a range instead of one number?: Because compost's density genuinely isn't predictable the way a mineral material's is. Oregon State University Extension's EM 9217 states a range of 800 to over 1,600 lb per cubic yard depending on moisture, particle size, and compaction — a dry, coarse load and a wet, fine load of the same volume can weigh nearly twice as much. Order by volume; treat the weight range as a delivery/truck-sizing estimate only.
Which depth should I use — topdressing, existing bed, amendment, or new bed?: It depends on the job. Lawn topdressing worked into turf is about ¼" (Penn State Extension). An existing bed's annual maintenance dose is ¼-1", defaulting to ½" (OSU EM 9308). A soil-amendment pass is 1-2", tilled into the top 4-6" (Penn State). A new bed being established from bare ground gets 3-4", incorporated into the top 8-12" (OSU EM 9308). These are four different jobs, not a disagreement between sources.
What happens if I apply too much compost at once?: Past UNH Extension's general ceiling of about 4 cubic yards per 1,000 sq ft, Oregon State University Extension's guidance notes that soluble salt levels in the root zone can rise enough to injure plants, with seedlings and transplants most susceptible. This calculator flags the ceiling automatically as a soft caution, not a hard stop — a single heavy pass on an established bed is different from broadcasting the same rate around new seedlings.
Why does thick, un-worked-in topdressing hurt my lawn?: Penn State Extension's turf-performance guidance warns that successive thick topdressing layers left on the surface without incorporation build up a mat of organic matter that dries out turf roots and restricts rooting — the opposite of the intended benefit. Topdressing is meant to be thin and worked in, not stacked pass after pass.
What's the difference between compost, topsoil, and garden soil?: Compost is fully broken-down organic matter — an amendment for soil that's already there, not a standalone growing medium. Topsoil is mineral-based soil used to build up grade or fill a bed from scratch. Garden soil blends start with topsoil and mix in compost and other amendments, sold pre-mixed for planting. Use compost to amend, topsoil or a blend to build.
How many bags of compost are in a cubic yard?: One cubic yard is 27 cubic feet, so that's 27 bags at 1 cu ft each, or 13.5 bags at 2 cu ft each. Bulk delivery is almost always cheaper than bagged past about a cubic yard, once packaging and handling costs are factored in.
Should I order based on the loose or settled depth?: Settled. Compost keeps breaking down and settling after it's applied, even more than topsoil does, since it's still actively decomposing. Order based on the depth you want after it settles, and let the waste factor cover the difference.