Concrete Calculator

1. Choose Shape: Slab or Footing. The choice changes labels to Number of slabs or Number of footings; both use the same rectangular volume calculation.
2. Enter the quantity of identical shapes. The calculator checks quantity from 1 to 1000 and requires a whole number.
3. Enter Length, Width, and Slab thickness or Footing depth, then select each unit.
4. Set Waste / overage %. The default is 10%, and 0% is allowed.
5. Choose Bag size: 40 lb, 60 lb, 80 lb, or Custom yield. For a custom value, enter Bag yield (cu ft) and check the product label.
6. Click Calculate. The result stays hidden until the values pass validation. Reset restores the default controls, clears the entered dimensions, and hides the result.

What the result shows

After a successful calculation, the result shows Concrete needed (with waste) in cubic yards, plus cubic feet, cubic meters, and bags. The bag statistic includes the yield used in ft^3/bag.

The Formula used block displays the formulas separately. Its assumptions table lists entered and converted values, intermediate volumes, waste allowance, bag yield, and bags needed; it does not place a formula on every row. Most values use fixed decimal places, while bags are displayed as a whole number.

Calculation formulas

The calculator converts length, width, and thickness/depth to feet before calculating:

• Volume per unit = Length x Width x Thickness
• Volume = Volume per unit x Quantity
• Total volume (with waste) = Volume x (1 + Waste % / 100)
• Bags = ceil(Total volume / Bag yield)

Bag count uses a ceiling calculation, so it rounds up to a whole bag.

Supported units and bag yields

• Length and Width: ft, in, yd, m, or cm.
• Slab thickness or Footing depth: in, ft, cm, or mm.
• Results: cubic yards, cubic feet, and cubic meters.
• Preset yields: about 0.30 cu ft for 40 lb, 0.45 cu ft for 60 lb, and 0.60 cu ft for 80 lb.
• Custom yield: enter a value in Bag yield (cu ft). Check the exact yield on the bag label.

Limits and assumptions

• The calculation assumes uniform rectangular dimensions and one thickness/depth for each shape.
• Waste / overage % is applied as a simple percentage to the calculated volume.
• Length, width, and thickness/depth must be greater than zero. Waste is checked from 0 to 50, and bag yield from 0.01 to 10 cu ft.
• Quantity is checked from 1 to 1000 and must be a whole number.
• The calculator does not model irregular or tapered dimensions, reinforcement displacement, site-specific conditions, live pricing, supplier data, or mix designs.
• The result is not certified engineering, structural, or purchasing advice.

Copy or download the result

Click Copy result to copy a plain-text summary to the clipboard. Click Download result (.txt) to save the same summary as a .txt file. The summary includes inputs, intermediate values, final volumes, bag yield, bag count, the formula, and the tool disclaimer.

Calculation and page data behavior

The concrete calculation runs in the page JavaScript from the values entered into the controls; the calculator script does not submit those calculation inputs to a server. The page also loads Ahrefs and Google Analytics scripts, and the separate newsletter form submits an email to /assets/subscribe.php when you use it.

Frequently Asked Questions