Concrete Beam Calculator

Calculate concrete volume, weight, bags, formwork, and rebar for rectangular and T-beams. Live 3D visualization updates as you type.

Total span
Cross-section width
Vertical depth
Number of beams
Typical: 5-10%
Affects weight calculation
Total Concrete Volume Primary 0.56 cu yd
In Cubic Feet 15.0 cu ft
In Cubic Meters 0.42 m³
Estimated Weight 2,250 lbs
60 lb Bags 34 bags
80 lb Bags 25 bags
Formwork Area Unique 45.0 sq ft
Rebar Estimate (1%) Unique 112 lbs
With 10% Waste 0.61 cu yd
Estimated Cost $70 – $92
How to Use
  1. Select your beam type (Rectangular or T-Beam)
  2. Choose your unit system (Imperial or Metric)
  3. Enter the beam's length, width, and height
  4. For T-Beams, enter flange width and thickness
  5. Adjust quantity if pouring multiple identical beams
  6. Set your waste percentage (10% is standard)
  7. Select concrete strength (affects weight)
  8. Results update live — check the 3D shape to verify dimensions
  9. Click "Download Report" for a branded PDF
Formula Used

Rectangular Beam:

  • Volume = Length × Width × Height
  • Weight = Volume × Density (150 lb/cu ft for 4000 PSI)
  • Formwork Area = 2 × (Width + Height) × Length
  • Rebar (1%) = Volume × 0.01 × 490 lb/cu ft

T-Beam:

  • Volume = (Length × Flange Width × Flange Thickness) + (Length × Web Width × Web Height)
  • Web Width = Beam Width
  • Web Height = Beam Height - Flange Thickness

Conversions:

  • 1 cu yd = 27 cu ft
  • 1 ft = 0.3048 m
  • 60 lb bag = 0.45 cu ft
  • 80 lb bag = 0.60 cu ft
Load Span Reference

Typical maximum spans for residential beams (4000 PSI concrete):

Beam Size Max Span
6" × 10" 8-10 ft
8" × 12" 10-12 ft
10" × 16" 12-15 ft
12" × 18" 15-18 ft
12" × 24" 18-22 ft

* Consult a structural engineer for actual load calculations.

FAQ

How much does a concrete beam weigh?

Standard concrete weighs approximately 150 lbs per cubic foot. A typical 10ft × 12in × 18in beam weighs about 2,250 lbs.

Do I need to account for rebar volume?

Rebar typically occupies less than 2% of beam volume, so it's negligible for material ordering. We estimate rebar weight separately using a 1% steel ratio rule of thumb.

What waste percentage should I use?

Use 5% for experienced crews with precise formwork, 10% for standard pours, and 15% for complex forms or inexperienced crews.

What is formwork area?

Formwork is the temporary mold for pouring concrete. The formwork area is the total surface area of the sides and bottom of the beam that needs to be formed. This helps you estimate lumber and plywood costs.

Can this calculator handle T-beams?

Yes! Select "T-Beam" from the beam type selector and enter the flange width and thickness in addition to the web dimensions.