Potting Mix and Planter Volume Calculator

This potting mix and planter volume calculator estimates how much potting mix a pot, trough planter, round planter, or tapered flower pot needs. Enter dimensions in centimetres or millimetres, choose the planter shape, adjust wall thickness, quantity, below-rim allowance, and bag size. Results show litres per planter, total litres, cubic metres, and approximate bag counts.

Planter setup
Measurements
External dimensions
Project settings

Estimates are for planning potting mix quantities only. Root ball size, drainage setup, false bases, wall thickness, and below-rim planting depth can change the final amount required. For balconies, rooftops, or suspended slabs, confirm planter loads with a qualified professional.

What the calculator estimates

The calculator supports rectangular trough planters, planter boxes, round pots, cylinder planters, and tapered flower pots with round or square openings. It can estimate:

Measuring the planter

Internal dimensions give the closest potting mix estimate. If only external dimensions are available, enter the outside measurements and add the wall thickness so the calculator can reduce the internal volume.

For rectangular troughs and planter boxes, enter length, width, and height.

For round planters and cylinder pots, enter diameter and height.

For tapered flower pots, enter the top opening, base, height, and whether the opening is round or square.

Planning potting mix for larger planters

Oversize planters, long troughs, and commercial planter projects can require a significant amount of potting mix once soil volume, plant size, water, drainage, and access are considered together. The calculator gives a volume estimate, but finished weight will vary by potting mix, water content, plant size, drainage material, and planter material.

For larger outdoor planters, compare the result with delivery access, surface protection, drainage position, and the final planted location.

Planter ranges to compare

Contact the showroom for availability, delivery, or advice.

Frequently asked questions

  • How do I calculate potting mix for a planter?

    For a rectangular planter, multiply internal length × width × height in centimetres, then divide by 1,000 to estimate litres. For round pots, calculate the cylinder volume from diameter and height. The calculator handles rectangular, round, and tapered planter shapes.

  • How much potting mix do I need for a 100cm × 40cm × 40cm trough planter?

    A 100cm × 40cm × 40cm trough planter holds about 160 litres before any allowance. With a 10% allowance for planting depth, root ball, or drainage setup, the estimate is about 144 litres, or roughly three 50 litre bags.

  • Should I measure inside or outside the pot?

    Internal measurements give the closest estimate. If you only have external dimensions from a product specification, enter the external measurements and add wall thickness so the calculator can adjust the volume.

  • What is the difference between litres and cubic metres?

    One cubic metre equals 1,000 litres. Litres are useful for bagged potting mix. Cubic metres are useful for larger planter projects, bulk mix estimates, and commercial planning.

  • Does the calculator include drainage layers or false bases?

    The calculator estimates volume from dimensions, then lets you subtract an allowance. Use the allowance field for below-rim planting depth, drainage setup, false bases, or root ball displacement.

  • Can the calculator estimate potting mix for tapered flower pots?

    Yes. Select the flower pot / tapered option, then enter the top opening, base, height, and whether the opening is round or square.

  • Can it calculate several matching planters at once?

    Yes. Enter the quantity of matching planters and the calculator will show the total litres, cubic metres, and approximate bag count.

  • How many bags of potting mix do I need?

    The calculator estimates bag counts for 25 litre, 30 litre, and 50 litre bags based on the planter volume and any below-rim allowance you set. Results are approximate — always round up when purchasing.

  • Does the calculator estimate finished planter weight?

    No. It estimates potting mix volume only. Finished weight depends on planter material, potting mix, water content, plant size, drainage material, and any false base.