Soil for Circular Planter

The Soil for Circular Planter calculator computes the volume and associated amount of soil for a circular planter (tapered or straight) based on the (t) top diameter, (b) base diameter and (h) height (see diagram).   

INSTRUCTIONS: Choose units and enter the following interior dimensions:

• (t) Top Diameter
• (b) Base Diameter (Note: this should match Top Diameter if container has vertical sides.)
• (h) Height of Planter or Depth of Contents in Planter

Soil Volume (V): The calculator returns the volume in cubic feet.  However, this can be automatically converted into other volume units via the pull-down menu next to the answer.  The calculator also returns the number of soil bags of the following sizes:

• 1 ft³
• 1.25 ft³ 
• 2.5 ft³  
• 8 quarts
• 32 quarts
• 64 quarts

IMPORTANT NOTE: To compute the amount of soil needed in the planter, use the interior dimensions of the container, and use the top diameter associated with how high you want to fill the container.  If you wish to fill to the brim, it is the full inner height.

The Math / Science

The formula for the volume of a circular planter is as follows:
                 `v = 1/12⋅π⋅h⋅(t^2+t⋅b+b^2)`

This answers the following questions:

1. How much soil will my planter hold?
2. How much water will my container hold?
3. How much potting soil do I need?

If you do not intend to fill the container to the top, this formula will over estimate unless you use a height (h) and top (t) that match your expected top surface inside the container.  Unless it's a very large container, and/or you are only using a small portion of the container, the overage should be small.

Potting Mix and Garden Soil

Potting Mix is combination of organic materials (e.g., peat moss, aged bark and pumice) but no soil (dirt) that is used in lieu of potting soil to improve drainage.  Because potting mix has no soil, it tends to be lighter than potting soil and provides a more sterile medium for plants with fewer disease carrying agents.  Potting mix is most commonly recommended for plants in containers, and potting mix is particularly desirable for starting seeds.  Garden Soil is a gardening product sold that contains natural soil (dirt) comprised of mixture of loam, clay and sand.  Garden soil is often used in raised gardens or planters as a healthy and easy medium for plants and seeds on top of the natural soil in one's yard.  Garden Soil differs from Potting Mix in that garden soil contains real soil (dirt), where Potting Mix does not.

Potting Mix and Garden Soil Price Survey

vCalc conducts a periodic pricing survey from nationally advertised retailers for various materials.  The current Garden Soil Price Survey sample information for Garden Soil and Potting Mix is as follows:

• Date: 5/14/24
• Store: Menards
  • Garden Soil (1 ft³): $6.49
  • Garden Soil (1.5 ft³): $7.49
  • Garden Soil (2 ft³): $9.99
  • Potting Mix (1.25 ft³): $13.71
  • Potting Mix (2.5 ft³): $27.43

Always use local pricing!  There is NO implied guarantee that these prices are available in your area or that products will be available.  This pricing is purely provided for estimation convenience.

Raised Garden and Planter Soil Calculator

• Soil for Box Planter: Computes the soil volume of a rectangular box shaped raised planter.
• Soil for Circular Planter: Computes the volume and associated amount of soil for a circular planter (tapered or straight) based on the top diameter, base diameter and height.
• Soil for Tapered Rectangular Planter : Computes the volume and associated amount of soil needed for a tapered rectangular planter based on the top and bottom side lengths and height.
• Soil for Polygon Shaped Planter: Computes the volume of soil needed for a polygon shaped planter based on its shape (number of sides) and dimensions including the length of the sides and the height (depth).
• Soil for Triangular Planter: Computes the volume and associated amount of soil for a triangular shaped planter based on the side lengths (a, b, c) and (h) height.
• Soil for Hexagon Planter: Computes the volume and associated amount of soil for a hexagon shaped planter based on the length of the sides and height.
• Soil for Octagon Planter: Computes the volume and associated soil amount for an octagon planter based on the length of the sides and the height. 
• Soil Needed for 3 Tier Raised Garden: Computes the amount of garden soil or potting mix needed for a three tier (step) raised garden based on the dimensions of the tiers.  
• Cost of Soil: Computes the cost of a volume of soil base on unit price.
• Water Requirement to Prepare Soil: Estimates the minimum and maximum water range for plant growth to apply to initially moisten soil so that plants will not suffer from over or under watering.
• Conversions to Common Kitchen Units:  This takes any volume measurement (you choose the units) and converts it into house-hold kitchen units.  For example, 0.9 ft³ turns into 6 Gallons, 2 Quarts, 1 Pints, 1.5 Cups, 3 Tablespoons and 1.54 teaspoons.  This is useful in measuring soil and nutrient supplements.

IMPORTANT NOTE: Use the interior dimension of the planters and a height to match the depth of soil desired.   

Other Garden Calculators

• Greenhouse Calculator
• Mulching and Landscaping Fabric Calculator