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Raised Bed Soil Calculator

Find how much soil fills one or more raised beds or planters, in cubic feet, cubic yards, liters and bags.

Level: Grades 7–8

  • Common Core standard 7.G.B.6Solve real-world and mathematical problems involving area, volume and surface area of two- and three-dimensional objects composed of triangles, quadrilaterals, polygons, cubes, and right prisms.
  • Common Core standard 8.G.C.9Know the formulas for the volumes of cones, cylinders, and spheres and use them to solve real-world and mathematical problems.
Printable worksheet

Raised Bed Soil Calculator

Know the answer you need? Pick an input to work backward.

Inputs
Units
Bed or container shape

How deep you will fill it, measured inside the walls.

Bagged garden soil is often 1, 1.5 or 2 cubic feet.

Loose soil sinks as it is watered. 10–20% extra is a common allowance.

Result

Soil to buy

35.2 ft³

Buy about 35.2 ft³ (1.3 cubic yards) of soil, or 24 bags of 1.5 ft³.

Bags of 1.5 ft³
24
In cubic yards (bulk)
1.3 yd³
In cubic meters
1 m³
Volume before the settling allowance
32 ft³

See the step-by-step solution ↓

Step-by-step solution

  1. Area inside the bed = length × width

    8×4=32 ft²

  2. Volume of one bed = area × depth (inches ÷ 12 gives feet)

    32×1212=32 ft³

  3. Multiply by the number of beds

    32×1=32 ft³

  4. Add 10% for settling

    32×1+0.1=35.2 ft³

  5. Convert to cubic yards for a bulk order (27 ft³ in 1 yd³)

    35.227=1.303704 yd³

  6. Divide by the bag size, then round up to whole bags

    35.21.5=23.466667=round up → 24

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find out how much soil you need to fill a raised bed or large pot, in cubic feet and in bags. Filling a raised bed takes more soil than most people expect. A single 8 by 4 foot bed filled a foot deep holds 32 cubic feet, which is more than twenty typical bags. Knowing the volume before you shop lets you compare bagged soil against a bulk delivery and avoid a second trip.

This calculator works for rectangular beds and for round beds or containers such as half barrels and large pots. Enter the inside measurements, the depth you plan to fill, and how many identical beds you have. A settling allowance is added because loose soil sinks once it is watered, and the result is given as a volume and as a whole number of bags.

Where it's used

Why this math matters outside the classroom:

  • Garden beds. A 4 × 8 ft raised bed filled 12 in deep needs 32 ft³, about 1.19 cubic yards of soil.
  • Bag counts. That 32 ft³ works out to 21.3 bags of 1.5 ft³, so the gardener buys 22.
  • Round planters. A planter 24 in across and 18 in deep holds π × 1² × 1.5 ≈ 4.7 ft³ of potting mix.
  • Settling allowance. Gardeners add a percentage, such as 10%, to cover soil that settles after the first few waterings.
  • School gardens. Teachers planning several identical beds multiply one bed's volume by the number of beds before ordering bulk soil.

Grade level and standards: Grades 7–8; Common Core State Standards for Mathematics 7.G.B.6, 8.G.C.9. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose US units (feet, inches, cubic-foot bags) or metric units (meters, centimeters, liter bags).
  2. Pick a rectangular or round shape and enter the inside length and width, or the inside diameter.
  3. Enter the depth of soil, the number of identical beds or containers, and the size of one bag.
  4. Adjust the settling allowance if you like, then read the volume to buy and the bag count.

What the inputs mean

Soil depth
Measure inside the walls, from the ground or the base of the container up to where the soil will stop. Leaving an inch or two below the rim makes watering easier.
Bag size
The volume printed on the bag. Many garden and raised-bed soils come in 1, 1.5 or 2 cubic foot bags.
Number of identical beds or containers
Use this for a row of matching beds or a set of identical pots. For beds of different sizes, run each size separately and add the totals.
Extra for settling
Fresh, fluffy soil and compost compact after the first few waterings. A 10–20% allowance keeps the bed close to full; set it to 0 if you are measuring settled soil.

Formula and method

area = length × width   or   area = π × (diameter ÷ 2)²
volume of one bed = area × depth
soil to buy = volume of one bed × number of beds × (1 + allowance % ÷ 100)
bags = soil to buy ÷ bag size, rounded up
1 yd³ = 27 ft³;  1 ft³ = 0.028316846592 m³;  1 m³ = 1,000 L

Each bed is treated as a box with straight walls, so its volume is the floor area multiplied by the fill depth. π (pi) is about 3.1416, the number that links a circle's width to its area. The depth is converted from inches or centimeters to feet or meters first so that every measurement is in the same unit.

The allowance is applied once to the total, and the bag count is rounded up because bags are sold whole. Tiny rounding errors from computer arithmetic are removed first, so an exact result is never pushed up by one bag.

Round containers are treated as cylinders. Pots that taper toward the base hold a little less than a cylinder of the same top width, so the result for tapered pots leaves some spare.

Worked example

One raised bed measures 8 ft by 4 ft inside and will be filled 12 inches deep, with 10% extra for settling and soil sold in 1.5 ft³ bags.

  1. Area: 8 × 4 = 32 ft².
  2. Volume: 32 × (12 ÷ 12) = 32 ft³.
  3. With 10% extra: 32 × 1.1 = 35.2 ft³.
  4. In cubic yards: 35.2 ÷ 27 = 1.30 yd³.
  5. Bags: 35.2 ÷ 1.5 = 23.47, which rounds up to 24 bags.

Result: Buy about 35.2 ft³ of soil (1.30 cubic yards, or 1.00 m³), which is 24 bags of 1.5 ft³.

Understanding the result

Once a project needs more than about one cubic yard, a bulk delivery is often cheaper than bags. Ask the supplier for the price per cubic yard and compare it with the bag total.

Many gardeners fill beds with a blend, such as topsoil mixed with compost. The total volume is the same however you split it; multiply the result by each ingredient's share to get the amount of each.

Assumptions and limitations

  • Every bed or container has straight walls and the same inside size.
  • The bag volume on the label is the volume the soil will fill.
  • One settling allowance applies to the whole order.
  • Sloping ground, L-shaped beds and tapered pots are approximated; split complex shapes into rectangles and circles.
  • Space taken by drainage layers, roots or plants already in the bed is not subtracted.
  • Soil keeps settling and breaking down over seasons, so later top-ups are not included.

Frequently asked questions

How many bags of soil fill a 4 × 8 raised bed?

At 12 inches deep the bed holds 32 ft³. That is about 22 bags of 1.5 ft³ before any allowance, or 24 bags with 10% extra for settling. At 6 inches deep you need half as much.

How deep should a raised bed be filled?

Many vegetables grow well in 8 to 12 inches (20 to 30 cm) of soil, and deep-rooted crops appreciate more. If the bed sits on loosened ground, roots can also grow down into the soil underneath, so a shallower fill can still work.

Can I use this for pots and planters?

Yes. Choose the round shape for pots or barrels and enter the inside diameter at the top, or use the rectangular shape for troughs and window boxes. Set the number of containers to fill a whole set at once.

How many cubic feet are in a cubic yard of soil?

Twenty-seven, because a yard is 3 feet and 3 × 3 × 3 = 27. A cubic yard is also about 0.765 m³, or 765 liters.

How this calculator is checked

Method: Prism and cylinder volume (area × depth) with exact US–metric factors; percentage allowance; bag count rounded up after removing floating-point noise. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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