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Garden & planters

Tapered pot volume calculator

A pot that widens uniformly does not have the same cross-section at every height. For a partial fill, the calculation first finds the diameter at the fill level, then uses the volume of the corresponding conical frustum. All dimensions are internal.

Your project measurements

Metric units
cm
cm
At least as large as the base diameter. Equal diameters give a cylinder.
cm
Model with straight sides and circular cross-sections, without an internal rim.
cm
Measured from the top rim down to the fill level.
L

Need a starting point? The initial values are an example.

YOUR ESTIMATE

21.99 L

Pot volume to fill

Tapered pot section: height 30 cm; fill height 30 cm.Top: 40 cmBase: 20 cmAxial sectionHeight: 30 cmFill: 30 cmClear: 0 cmD at fill: 40 cmIndicative diagram21.991 L
Fill height30 cm
Diameter at fill level40 cm
Total internal capacity21.99 L
Unfilled volume0 L
Bags needed2 bags
Purchased volume40 L

Measure the inside: the model assumes circular cross-sections, a flat base and straight sides that widen uniformly.

Root balls, other layers, rims and settling are not deducted. The geometric result does not choose the growing medium.

Understand the calculation
  1. Fill height: 30 − 0 = 30 cm.
  2. Diameter at fill level: 20 + (40 − 20) × 30 ÷ 30 = 40 cm.
  3. Volume: π × 30 × (20² + 20 × 40 + 40²) ÷ 12000 = 21.991 L.
  4. 21.991 L ÷ 20 L per bag, then round up. Number of bags: 2.

The estimate depends on your measurements and entered inputs. PDF output uses your browser’s Save as PDF option.

MetraNest · https://metranest.com/en/calculators/tapered-pot/ · Méthode : Diamètre rempli = diamètre du fond + (diamètre du haut − diamètre du fond) × hauteur remplie ÷ hauteur totale. Volume en L = π × hauteur remplie × (diamètre du fond² + diamètre du fond × diamètre rempli + diamètre rempli²) ÷ 12000, avec les longueurs en cm.

Check the shape of the pot

The model assumes a flat circular base, circular cross-sections and straight sides between the base and the top. Measure the internal diameters without including wall thickness. A bulging or stepped pot, or one with an internal reservoir, does not match this shape exactly.

Find the diameter at the fill level

The filled height is the internal height minus the headspace left at the top. In this model, the diameter increases in proportion to height. A pot filled halfway up does not therefore necessarily contain half its capacity: the lower half is narrower.

Compare geometric volume and purchasing quantity

The volume is converted from cubic centimetres to litres, then rounded up to bags of the specified size. Roots, root balls and other layers are not deducted automatically. Settling may also change the quantity used. Keep these factors separate from the calculated internal volume and choose a growing medium suited to your project.

The formula
Fill-level diameter = base diameter + (top diameter − base diameter) × filled height ÷ total height. Volume in L = π × filled height × (base diameter² + base diameter × fill-level diameter + fill-level diameter²) ÷ 12000, with lengths in cm.

Half the height, not half the volume

For a pot 30 cm high, with a diameter of 20 cm at the base and 40 cm at the top, leaving 15 cm clear gives a filled height of 15 cm and a diameter of 30 cm at that level. The volume is 2.375π, or approximately 7.461 L. Total capacity is 7π, or approximately 21.991 L.

Details to check

  • Measure the internal diameter at both levels.
  • Keep the headspace height in the same unit as the pot.
  • Deduct known occupied volumes separately.

Frequently asked questions

What happens if the two diameters are equal?

The model becomes a cylinder. The diameter remains constant and the volume is proportional to the filled height.

Why not multiply the capacity by the filled fraction?

The cross-section varies with height. In a tapered pot, upper layers contain more volume than layers of the same height at the base.

A method you can check · Content review :

Each tool shows its formulas and assumptions. Worked examples let you repeat the calculation and understand how rounding works.

See MetraNest’s method · Contact and corrections

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