Concrete Beam Calculator

1. Enter the beam length in feet, along the span.
2. Enter the width and depth in inches, from your plans.
3. Set the number of beams for identical beams, and a 5 to 10 percent waste allowance.
4. Pick a bag size for a bag count, then read the cubic yards to order.

Here is what each result line means:

A concrete beam calculator turns the length, width and depth of a beam into the amount of concrete to order. It is for rectangular beams: grade beams in a foundation, tie beams, lintels and headers over openings, and similar cast-in-place members.

A beam is a long rectangular prism, so its volume is length times width times depth. The tool converts feet and inches into cubic yards and bags and adds a waste allowance for form deflection and over-pour at the ends. To get the mix proportions right use the concrete mix calculator, and for the binder use the cement calculator.

Because a beam is a rectangular prism, its volume is simply length times width times depth, with every dimension in the same units. The tool works in feet and divides by 27 for cubic yards.

1. Convert the width and depth from inches to feet by dividing by 12.
2. Multiply length by width by depth for the volume of one beam in cubic feet.
3. Multiply by the number of beams, then add the waste allowance.
4. Divide by 27 for cubic yards, multiply by 0.0283168 for cubic meters, and divide cubic feet by the bag yield for a bag count.

Beams are almost always reinforced; size the bar grid with the concrete weight calculator for the placed weight.

Suppose you are pouring a grade beam 20 feet long, 12 inches wide and 18 inches deep, with 10 percent waste.

Calculation: the width is 12 / 12 = 1 ft and the depth is 18 / 12 = 1.5 ft. Volume = 20 x 1 x 1.5 = 30 cu ft, or 30 / 27 = 1.11 cu yd. Adding 10 percent waste gives 33 cu ft, about 1.22 cu yd and roughly 55 eighty-pound bags.

The lesson: a deep beam holds a surprising amount of concrete, because depth and width multiply along the whole span.

Depth

Depth usually governs a beam and it multiplies the whole length, so it moves the volume most. Confirm the depth before ordering.

Width

Width multiplies the volume directly too. A wider beam carries more concrete over the same span.

Length and Span

Length scales the volume one for one, so a long beam uses proportionally more. Measure the full poured length, including any bearing into supports.

Number of Beams

Repeating identical beams multiplies any per-beam error, so confirm one beam first, then set the count.

Rectangular concrete beams do different jobs, which changes how you measure and pour them.

For the delivered price of either pour, the concrete cost calculator in the related tools prices it by the yard.

Ordering Concrete for a Beam

Size the beam in cubic yards and add waste before you order, so you can pour each beam in one continuous run without a cold joint.

Pricing a Small Beam or Lintel

For a short lintel or header, the bag count shows how many bags to buy and whether hand mixing is realistic.

Planning Repeated Beams

Tie beams and joists are repeated members; the quantity field totals them so you order once for the whole set.

1. Mixing Up Inches and Feet

Enter length in feet and width and depth in inches, as the fields are labelled. Entering depth in feet shrinks the result twelvefold.

2. Swapping Width and Depth

Width and depth both multiply the volume, so swapping them gives the same total, but it matters for the forms and the bar layout. Keep depth as the vertical face.

3. Forgetting Bearing Length

A beam bears into its supports at each end, so the poured length is a little more than the clear span. Include the bearing.

4. Ignoring a Haunch or Drop

A thickened haunch or a drop panel holds extra concrete. Work those parts out separately and add them.

5. Treating the Estimate as a Design

Volume is not capacity. Beam size, span and reinforcement come from an engineer or code, not from this tool.

The arithmetic is exact; the usefulness depends on the dimensions, quantity and waste you enter.

Multiply the length by the width by the depth, all in feet, then divide by 27 for cubic yards and add 5 to 10 percent waste. A 20 foot beam 12 inches wide and 18 inches deep is 20 x 1 x 1.5 = 30 cubic feet, about 1.11 cubic yards before waste.

It depends on the size. A 20 foot grade beam 12 inches wide and 18 inches deep is about 1.11 cubic yards, or 1.22 with a 10 percent allowance, roughly 55 eighty-pound bags. Enter your own length, width and depth above for the exact figure.

Width is the horizontal face and depth is the vertical face. Both multiply the volume the same way, but depth usually governs a beam structurally, and the two must match the forms and the bar layout even though they give the same volume if swapped.

A 20 foot beam 12 by 18 inches is roughly 55 eighty-pound bags with waste, which is a lot to mix by hand, so a beam this size is usually ready-mix. The tool gives the bag count for your beam and bag size, rounded up.

Yes. Enter the opening width plus the bearing at each end as the length, and the lintel width and depth. Set the quantity if you have several identical lintels, and the tool totals the concrete.

Yes, 5 to 10 percent. Formed beams lose concrete to form deflection, the ends and spillage, and a cold joint in a beam is a weak point, so a margin keeps the pour continuous.

No. It estimates the concrete volume once you enter the size. The required beam depth, span and reinforcement come from your plans, local code or a structural engineer.

No. It estimates the concrete only. Beams are reinforced with bar and stirrups that you size separately from your drawings or with a rebar estimate.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• QUIKRETE Concrete Mix 1101 data sheet (QUIKRETE; bag yields 0.60, 0.45 and 0.30 cu ft).
• National Ready Mixed Concrete Association (NRMCA; ready-mixed concrete and ordering).
• American Cement Association (American Cement Association; reinforced concrete basics).