How the Concrete Calculator Works
The estimator multiplies the slab length, width, and thickness after converting the selected dimensions to meters. It adds the chosen allowance, then converts the volume to cubic yards and estimates bag count using the yield you enter.
Formula and method
Base volume = length × width × thickness. Order volume = base volume × (1 + allowance percentage). Bag count = order volume in cubic feet ÷ stated yield per bag, rounded up.
Tips for better estimates
Measure the inside dimensions of the formwork and use the actual bag yield from the product label. For large pours, compare the result with a ready-mix supplier’s volume recommendation.
Important limitations
This calculator models a rectangular pour only. It does not include footings, slopes, reinforcement displacement, uneven subgrade, truck minimums, or supplier-specific batching and waste requirements.