To be accurate, the estimator should carefully check all the plans and specifications for the project. Concrete often appears on drawings other than structural drawings, such as the need for equipment pads in the mechanical and electrical drawings, or curbs and sidewalks in the civil drawings.

When estimating structural concrete, pay particular attention to requirements for concrete additives, curing methods and surface treatments. Special consideration for climate conditions as well as hot or cold weather conditions must be included in your estimate. Also include requirements for concrete placing and finishing methods and equipment.

For accurate concrete estimating, the estimator must consider each of the following major components individually: formwork, reinforcing steel, ready-mix concrete, placement of the concrete mix, finishing of the surface, and curing.

Formwork is normally taken off in square feet (generally in square feet of area in contact with the concrete, as opposed to the actual area of forms used). Enough forms must be available for erection to make efficient use of the concrete placing equipment and crew. read more.

Reinforcing is normally taken off in tons of rebar, hundreds of square feet (CSF) of welded wire fabric, or pounds of pre-stressing strands. When estimating the amount of reinforcing steel, either bar or mesh, if no lap specifications are given, add 10% to your quantities for lapping, splices, and waste. read more.

Ready-mix concrete is normally taken off in cubic feet, but then converted to cubic yards, as this is the unit of measure that suppliers charge for.

Placing of ready-mix concrete is normally taken off in cubic yards for each of the placing methods (direct chute, conveyor, pump truck, and crane & bucket). When estimating the placement of concrete by direct chute, the forms available generally determine the volume of concrete placed per hour. The more you have available, the more concrete can be placed in the course of a day. When placing concrete by methods involving a bucket and crane, pumping system, conveyor belt system or other mechanical system, set up enough forms to keep the above systems productive for the entire day. Usually the cost for the use of the equipment for a full day will be charged to you even if you only use it for part of a day. read more.

Finishing the concrete surface is normally taken off in square feet and can include the top surface of flatwork as well as vertical walls and horizontal structure faces that will be exposed. A good rule of thumb for finishing concrete: allow 1,000 S.F. of slab per each cement finisher.

Curing is normally taken off in hundreds of square feet (CSF) for each of the curing methods (water curing, chemical compound membrane, and sheet membrane).

Additional Tips for Estimating Concrete

Concrete Block-outs
When estimating quantities of concrete for floor slabs or walls, do not bother to deduct small areas (two square feet or so) unless there are a large number of these areas, as this can take up more estimating time than the areas are worth. Also remember that you will be adding approximately 3% to the total volume for waste, thereby making these small areas even less significant.

Check All Plans
It cannot be stressed enough that all plans for concrete must be checked. Concrete has been known to show up in all sections of construction drawings in various forms and uses (e.g., equipment pads located only on mechanical or electrical drawings, grouting requirements on steel drawings, etc.). Assuming all concrete requirements are indicated on the structural and architectural drawings can be a costly error.

Testing Concrete
When estimating the amount of concrete compression testing that will be necessary for a project, figure on a minimum of one test per pour on smaller pours and a minimum of one test for each fifty yards of concrete placed. Each test should consist of taking a set of three cylinders minimum.

Drilling Anchor Bolts
Consider drilling anchor bolts into the concrete where design permits to save time, manpower, and materials on layout and templates during the pour.