This calculates the volume of a polygon shaped planter. Enter the dimensions of the planter including the number of sides (n), the length of one of the sides on the top (t) of the container, the length of one of the sides of the bottom (b) of the container and the (d) depth of the interior of the box (see diagram), then this formula will provide the volume of the container. This answers the following questions:
If you do not intend to fill the container to the top, this formula will over estimate unless you use a depth (d) 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.
A quick survey of Home Depot's and Lowe's web sites show that potting soil usually comes in a few standard size bags:
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.
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. This includes some useful industry data like potting soil pricing from national advertisers.
This formula is based on thein 3-D geometry.