The Tapered Rectangular Planter Volume calculator computes the volume of a tapered rectangular planter. Enter the measurements of the planter: (t) top side length, (b) bottom side length and (h) height of the interior of the box (see diagram), then this formula will provide the volume of the container. 
Tapered Rectangular This answers the following questions:
- How much soil will my box planter hold?
- How much water will my box container hold?
- 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) that matches 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.
Standard Units
A quick survey of Home Depot's and Lowe's web sites show that potting soil usually comes in a few standard size bags:
- 1 ft3
- 1.25 ft3
- 2.5 ft3
- 8 quarts
- 32 quarts
- 64 quarts
To get your answer in the number of bags needed, click the UNITS button labelled SYSTEM and select the bag size you wish. vCalc will convert your answer from standard volume units (e.g. cubic feet) to the number of bags of that size.
Other Planter Shapes
The volume of planter is based on its shape. Here are the pages for other shapes:
Or just use the single calculator with all of the shapes available in one place at Planter Calculator. This includes some useful industry data like potting soil pricing from national advertisers.
The Math
This formula is based on the volume of a cuboid in 3-D geometry.