Soil and Mulch Calculator

Volumes in cubic yards, bags counted honestly, soil classed by the triangle

Two tools share this page because gardens ask both questions. The first turns an area and a depth into a volume in cubic yards and cubic feet, a bag count at the bag size you actually buy, an estimated weight at the material’s typical density, and a settling allowance you set, because loose material compacts and a bed filled exactly to the line today sits below it next month. The second is a soil texture classifier: enter sand and clay percentages from a soil test (or a careful jar test) and it places the soil on the USDA texture triangle, silt by difference, with the honesty note that boundaries on that triangle are surveyed lines and near them a laboratory particle-size analysis is the referee.

Soil and mulch volumes
Soil texture (USDA triangle)

Disclaimer: This calculator gives estimates for general information only. It is not financial, medical or other professional advice. Densities vary with moisture and material source; soil texture classes near triangle boundaries are confirmed by laboratory analysis, not by any calculator.

What this calculator does

Soil and mulch are bought in a confusion of units: yards at the landscape yard, cubic-foot bags at the store, pounds on the delivery ticket. The volume tool holds them together with two stated bridges: density (weight per cubic yard, printed beside each material because wet topsoil and dry bark are different substances that happen to share a shape) and the settling allowance, which exists because a cubic yard spread loose is not a cubic yard a season later. The texture tool addresses the prior question, what the soil itself is: the USDA triangle is the standard map of soil behaviour, and a soil’s class predicts its drainage, workability and hunger better than any product label.

How to use it

  • Depth is a decision, not a default. Mulch suppresses weeds at about 3 in and wastes money and root oxygen at 6; raised beds want their full soil depth; a topdressing is a quarter inch with a different tool’s name. The worked examples argue the common cases.
  • Measure the bed you have, including its taper. Kidney beds and tree rings defeat rectangles; break them into a rectangle plus circles, run each, and add. The area and volume calculator linked below is the companion for odd shapes.
  • Bags versus bulk has a break-even. The two price fields let the page compare your local numbers directly; as a rough geography, bags win under about a cubic yard and lose quickly above it, before delivery fees argue back.
  • Texture percentages come from a test. A laboratory soil test reports them; the jar settling test estimates them at home well enough for class-level decisions, which is the level this classifier works at.

The methods

  • Volume = area × depth, in cubic feet and cubic yards (27 cu ft). Rectangle area is length × width; circle area is π × (diameter/2)².
  • Order volume = volume × (1 + settling%). Bags = order volume in cu ft / bag size, rounded up. Weight = cubic yards (before settling) × the selected typical density.
  • Texture: silt = 100 − sand − clay, and the class is read from the USDA texture triangle’s standard boundaries, including the sand-corner boundary equations (silt + 1.5 × clay against 15 and 30) that define sand and loamy sand.

Worked examples

The 10 by 4 bed in mulch. At 6 in deep for a new bed’s first fill, it holds 40 × 0.5 = 20 cu ft, or 0.74 cu yd: exactly 10 bags of 2 cu ft with no settling allowance, 11 with 10 percent, and about 444 lb of bark mulch at its typical density, which is why mulch goes home in a hatchback and topsoil, at over a ton for the same volume, sensibly arrives by truck.

The texture call. A soil test reading 40 percent sand and 20 percent clay leaves 40 percent silt, and the triangle places it squarely in loam, the class gardeners hope for: balanced drainage and workability. Move clay to 35 at the same sand and the class becomes clay loam, a different amendment conversation entirely, which is why three honest numbers beat the word “dirt” every time.

Reading your results

Read cubic yards as the bulk language and bags as the retail language for the same pile, and read the weight before choosing the vehicle: the density spread between mulch and sand is fourfold, and suspension and backs both notice. Read the settling allowance as next season’s top-up arriving early. And read a texture result near a boundary (within a few points of a class edge) as a range rather than a verdict, since sampling error alone can walk a soil across a line the triangle draws sharply.

Limitations

  • Densities are typical, moisture-ruled values. Rain-soaked mulch and kiln-dry compost depart widely from the printed figures; weights are planning numbers for vehicles and backs, not scale tickets.
  • Depths assume level beds. Sloped ground takes more material on the low side by geometry the single depth cannot see; measure an average depth or terrace the bed in your head before ordering.
  • The triangle classes mineral soil. Heavy organic matter, gravel content and salinity move real behaviour off the chart; a soil that is half gravel is a drainage fact first and a texture class second.
  • Bag volumes are nominal. Bagged products settle in the bag and are sold by the printed volume under packaging rules; the count here trusts the print, as buyers must.

Frequently asked questions

How deep should mulch be?

About 3 inches over soil is the working standard: enough to shade the surface, slow evaporation and discourage weed seed germination, not so much that water struggles to reach roots or crowns stay wet. Over existing mulch, top up the difference rather than adding a full depth (the volcano of mulch against trunks is a genuine tree-health problem, not a style choice). Fabric under mulch changes the depth conversation not at all, and the depth field takes whatever your surface honestly needs.

How many bags make a cubic yard?

Twenty-seven cubic feet, divided by the bag: 13.5 bags of 2 cu ft (so 14), 18 of 1.5, 27 of 1, or 36 of the 0.75 cu ft topsoil size. That arithmetic, against the bulk price per yard, is the entire bags-versus-bulk decision, and the calculator runs it with your local prices filled in because delivery fees and minimums move the answer more than any national average could.

What is the jar test and how good is it?

Shake soil and water in a jar, let it settle in layers (sand within minutes, silt over hours, clay over a day or more), and measure each layer’s share of the settled column. Done carefully it lands within a few percentage points of laboratory texture, comfortably accurate for choosing a class and an amendment strategy. Its known weakness is clay that stays suspended and organic matter that floats, both of which a pinch of dish soap (a dispersant) helps settle.

Can I fix clay soil by adding sand?

Not at garden scale, and the triangle shows why: moving a clay loam to a loam means shifting its percentages by tens of points, which takes sand volumes comparable to the bed itself, incorporated completely, and a half-hearted mix lands in the sandy clay loam region that behaves like neither, the famous recipe for homemade concrete. Organic matter, patient and repeated, is the amendment that works on clay, because it changes structure rather than ratios.

Related calculators

Method: volume from area and depth with an explicit settling allowance, bags at the selected printed size, weight at stated typical densities, and soil texture classified on the USDA triangle boundaries with silt by difference. Last reviewed: 15 October 2026.