A concrete order is only as good as the measurements behind it. Measure where the concrete will actually go, write every number down with its unit, and break complicated shapes into simple ones.
The general rules
- Measure inside the forms. The concrete fills the space between the boards, not the boards themselves.
- Measure thickness or depth of concrete only. Gravel bases are a separate material.
- Measure in several places. Ground is rarely flat. Take the depth at the corners and the middle and use the average.
- Keep units straight. The calculator accepts 10’ 6”, 10.5 ft, 126 in or 3.2 m and shows how it read each one, so check the line under every field.
Slabs, patios and driveways
Length × width × thickness. For an L-shape, measure it as two rectangles and add both as sections. For a round patio, measure the diameter straight through the center. If you know the area from a plan, use “Slab by area”.
Footings
For a continuous footing, add up the length of every run. Measuring along the center of the footing avoids double-counting corners. Width and depth are the size of the trench or form.
Post holes
Measure the hole’s diameter and depth, the gravel you’ll put in the bottom, and your post’s actual size (a 4×4 measures 3½ in). QUIKRETE recommends a hole about three times as wide as the post and 1/3 to 1/2 as deep as the post’s height above ground, plus 6 in for gravel.
Tubes and columns
Use the tube’s inside diameter (printed on the form) and the full height to be filled, from the bottom of the hole to the top of the tube.
Walls and steps
For walls, measure length, height from the top of the footing, and the gap between the forms. Note each door or window opening. For steps, count the risers, then measure the rise, run and width.
Cut-outs and odd shapes
Anything inside the area that won’t be concrete (a tree, a drain box) can be added as a section set to subtract. Odd shapes can almost always be broken into rectangles, triangles and circles.
Then add a margin
NRMCA advises ordering 4% to 10% more than your measured volume. The concrete calculator adds this for you.