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Garden & Landscape

Mulch, Topsoil & Gravel Calculator

Work out how many cubic yards of mulch, topsoil or gravel an area needs at the depth you're spreading or filling to.

Calculate your bulk material

For one rectangular area — a bed, a border, a path or a raised bed. Length and width in feet, depth in inches. The estimate updates as you type.

Material

The volume is worked out the same way for all three. Your choice sets the wording of the result and is a reminder that depth and settling are judged per material.

Area and depth
ft
ft
in
×

For a raised bed, measure the inside of the frame rather than its outer dimensions — the boards themselves take up space — and enter the depth you are filling to, which is usually below the rim. Use the count for several identical areas, such as three matching beds.

Planning allowance
%

Starts at 0%, which gives the measured volume exactly. Raise it for settling, compaction, uneven ground and spread loss — how much depends on your material, how it is laid and your own site, so no default figure is suggested here.

Buying in bags?
cu ft

Optional. Enter the cubic feet printed on the bag and you get a bag count as well. Leave it blank if you are ordering loose by the cubic yard.

The method

  1. 01

    Area to cover

    length (ft) × width (ft) × number of areas

    For an irregular bed or border, split it into rectangles and run each one separately. Several identical areas — three matching raised beds, say — can go through as a count instead.

  2. 02

    Convert depth to feet

    depth (in) ÷ 12

    Spread and fill depths are normally talked about in inches; converting to feet lets the depth multiply directly against an area in square feet.

  3. 03

    Volume

    area (sq ft) × depth (ft)

    Gives the volume in cubic feet, before any allowance.

  4. 04

    Add a planning allowance

    volume × (1 + allowance)

    Optional, and 0% is a valid answer. It covers settling, compaction, uneven ground and spread loss — all of which depend on the material and the site, so the calculator suggests no figure of its own.

  5. 05

    Convert to cubic yards

    cubic feet ÷ 27

    Loose bulk material is sold and delivered by the cubic yard, so this is the figure to quote a supplier.

  6. 06

    Bags, if buying bagged

    round up (cubic feet ÷ bag size in cubic feet)

    Rounds up to the next whole bag, since bags can't be split. This is the only figure the calculator rounds — the cubic feet and cubic yards above keep full precision.

Worth knowing

  • The arithmetic is the same for mulch, topsoil and gravel. What differs is the depth you choose and how much the material settles or compacts once it's down.
  • Measure a raised bed on the inside of the frame, and fill to below the rim rather than level with it — filling to the top tends to wash and spill over.
  • Gravel is usually compacted deliberately, so the loose volume delivered is more than the finished depth suggests. Topsoil sinks as it's watered in. A loose mulch top-up barely settles at all. Judge the allowance from the material and the job.
  • There's no universal bag size for bulk material, so a bag count only means something against the cubic feet printed on the bag you're actually buying.
  • Some suppliers price loose material by weight rather than volume. Converting cubic yards to tons needs the density of that specific material, which this calculator doesn't assume — ask your supplier.
  • Laying a gravel sub-base under a slab? Work the gravel out here, and use the Concrete Calculator for the slab itself.

Bulk material calculator examples

The three jobs this calculator was built for. Every depth and allowance below is an assumption chosen to make the arithmetic concrete, not a recommendation.

Job
Spread mulch
Bed
20 × 10 ft
Depth
3 in
Allowance
0%
  1. Area20 × 10 = 200 sq ft
  2. Depth in feet3 ÷ 12 = 0.25 ft
  3. Volume200 × 0.25 = 50 cu ft
  4. Convert to cubic yards50 ÷ 27 = 1.85 cu yd
  5. In 2 cu ft bags50 ÷ 2 = 25 bags

1.85 cubic yards, or 25 bags.

A loose mulch top-up settles very little, so this example adds nothing on top. The bag count is the only figure rounded — and here it happens to divide exactly.

Job
Fill raised beds
Each bed
8 × 4 ft
Fill depth
10 in
Beds
3
  1. Area8 × 4 × 3 = 96 sq ft
  2. Depth in feet10 ÷ 12 = 0.83 ft
  3. Volume96 × 0.83 = 80 cu ft
  4. After 5% allowance80 × 1.05 = 84 cu ft
  5. Convert to cubic yards84 ÷ 27 = 3.11 cu yd

3.11 cubic yards of topsoil.

The 8 × 4 ft is the inside of the frame, and the 10 in fill depth sits below a 12 in rim. The 5% here is an assumed allowance for topsoil sinking as it's watered in.

Job
Lay a gravel path
Path
30 × 3 ft
Depth
4 in
Allowance
10%
  1. Area30 × 3 = 90 sq ft
  2. Depth in feet4 ÷ 12 = 0.33 ft
  3. Volume90 × 0.33 = 30 cu ft
  4. After 10% allowance30 × 1.10 = 33 cu ft
  5. Convert to cubic yards33 ÷ 27 = 1.22 cu yd

1.22 cubic yards of gravel.

The 4 in is the finished, compacted depth. The 10% is an assumed allowance for the loose material compacting down — gravel is the material where this matters most.

What the planning allowance is covering

The calculator starts at 0%, which gives the volume your measurements describe. Anything above that is covering something specific.

What it coversWhen it matters
CompactionGravel and similar aggregates laid to a compacted depth
SettlingTopsoil and compost-rich fills, which sink as they water in
Uneven groundDips and ruts that hold more than a flat area would
Spread lossMaterial lost off the edge of a bed, a barrow or a tarp

No default is offered: a loose mulch top-up barely settles, a deliberately compacted gravel base does, and topsoil is somewhere in between and depends on how much organic matter is in it. Judge the figure from your material and your site, or ask the supplier what they see.

How deep should you go?

Depth is the input that moves this result most, and it isn't something a calculator can decide for you.

A mulch layer is chosen for weed suppression and moisture retention without smothering what's planted; a topsoil fill is chosen for what the plants need to root into; a gravel path or base is chosen for the traffic it carries and what sits beneath it. The right depth depends on the material, the plants, the drainage and what the surface has to do, so take it from the product's own guidance, a local supplier, or the planting or paving spec you're working to. This calculator works out the volume for a depth you provide.

Bulk delivery vs. bags

The same volume, bought two different ways — and only one of them rounds.

Loose material is sold by the cubic yard and delivered as a fractional quantity, so the cubic-yard figure above is used as it stands — there are 27 cubic feet in a cubic yard, which is why the calculator works out cubic feet first and converts. Bags are different: you buy whole ones, so that figure rounds up. Bag sizes vary by product and by material, so enter the cubic feet printed on the bag you're buying rather than assuming a standard size. Suppliers also often set a minimum delivery and a load increment, which can make a small bulk order more expensive per yard than it looks — worth comparing against the bag count before deciding.

Mulch, topsoil and gravel calculator FAQ

How many cubic yards of mulch do I need?
Multiply the area in square feet by the depth in feet, then divide by 27. A 20 × 10 ft bed at 3 in deep is 200 × 0.25 = 50 cubic feet, which is 1.85 cubic yards. The depth is the part you choose — the calculator above does the rest.
How much topsoil does a raised bed take?
Measure the inside of the frame rather than its outer dimensions, and use the depth you're filling to rather than the full height of the bed — filling level with the rim tends to wash and spill over. An 8 × 4 ft bed filled to 10 in is about 80 cubic feet, or just under 3 cubic yards, before any allowance for the fill settling.
How many bags is a cubic yard?
It depends entirely on the bag. A cubic yard is 27 cubic feet, so it's 27 divided by the cubic feet printed on the bag — 14 bags at 2 cubic feet each, 54 at half a cubic foot. There's no universal bag size for bulk material, which is why the calculator asks for yours.
Should I add extra for settling or compaction?
Often, but there's no single figure. Gravel laid to a compacted depth needs more loose material than the finished depth suggests; topsoil sinks as it's watered in; a loose mulch top-up barely settles. The calculator starts at 0% deliberately and lets you set the allowance for your material and site.
Is this the same as the Concrete Calculator?
The volume arithmetic is the same — area × depth, converted to cubic yards. What differs is everything around it. Concrete is a single poured material with a waste allowance for spillage and over-excavation, and it's ordered as a fractional cubic-yard pour. Bulk material comes in three kinds, is often bought in bags, and its allowance is about settling and compaction. If you're pouring a slab, use the Concrete Calculator; if you're filling a bed or laying a path, use this one.
How many tons of gravel is that?
Converting volume to weight needs the density of that specific material, which varies with the stone, its size and how wet it is. This calculator deliberately doesn't assume a figure — if your supplier prices by the ton, give them the cubic yards and let them convert.

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