This calculates the volume of a triangular shaped planter. Enter the length of the three sides of the planter (a,b,c) and the (h) height of the interior of the container (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.
This formula is based on thein 3-D geometry.