Before we learn how to calculate the stairs' concrete volume, we first need to know the different parts of a stair. Though we have a separate stair calculator that tackles that, here we will introduce some other stair dimensions: the stairs' carriage and throat depth.
Though the carriage may resemble a stair stringer, they are now different since we're dealing with concrete stairs.
Apart from the common step's riser and run (which are the distance between two adjacent steps, vertically and horizontally, respectively), we'll also need to consider the carriage because that connects the steps together, as shown colored light green in the illustration below:
The carriage will also encase the reinforcing steel bars when needed, especially if you want to keep a storage space underneath the stairs.
On the other hand, the throat depth is basically the thickness of the carriage. It is also the perpendicular distance between the underside of the carriage and the inner joint between a tread and its consecutive riser.
Now that we've discussed the different details of the stairs we need for the basic calculation of the stairs' concrete, let's now learn how to calculate how much volume of concrete we'll need for a concrete stair project.