How to Measure for a Concrete Slab
If you're intending to build a concrete slab, you need to know exactly how much concrete you'll need. Remember, though, that concrete is a three-dimensional substance, and measuring for this factor makes it a little more complicated than measuring the area of the slab. You've got to get its volume.
For this project, you will need:
- Measuring tape
- Chalk or stakes
- Trace the area you're intending to fill with concrete with a straight chalk line, or else deploy stakes to keep your later work straight. If the area you're working with is for some reason not a geometric shape, instead trace an approximate and regular shape around the region, which is easier to work with. This will result in some extra concrete in your calculations, but will make those calculations much easier.
- Measure the depth of the region. For many concrete slabs, the depth of the region to be filled will be more or less uniform, and one measurement is sufficient. If there is a sharp variance in depth, measure these different regions separately. If there is only a gradual difference in depth, you can use the deepest point in the region for your single measurement.
- Calculate the volume of the region. Find the area of your chalked region, and multiply by the depth of the region to be filled with concrete. Ideally, this is means finding the area of a regular geometric shape, and multiplying it by a uniform depth. Remember to keep your units straight in this step. Concrete slabs rarely have a thickness in feet or meters, but converting your measurements into these units can make things much easier. For example: a twenty foot by ten foot region, four inches deep, has a volume of 20x10x(4/12), or 66.66 cubic feet.
- Convert your measurement. Concrete is usually sold in predefined amounts unless you're calling a mixer-truck. Convert your measurements into whatever regional standard concrete uses in your area to determine how many purchases you need to make. You probably won't be able to get a precise number, but don't be afraid of rounding up. Irregularities mean you might be using more concrete than you calculated, and having more on hand is certainly better than running out mid-project!