Density Constants
Standard Bag Yields
*Approximate yield after water addition.
Water Ratio Tip
Always start with 3/4 of targeted water. Excess water significantly reduces structural PSI.
Adding a 10% waste factor is industry standard to account for spills, uneven forms, and consolidation.
Concrete Column Calculator Logic
Frequently Asked Questions
Muhammad Shahbaz Siddiqui
Founder, TheCalculatorsHub
How I worked out the concrete volume for deck support columns
I was setting 4 cylindrical concrete footings for a small deck structure, each 300 mm in diameter and 600 mm deep. Mixing by hand, I needed to know the exact number of 20 kg bags to buy before starting. Getting it wrong in either direction meant either an interrupted pour or wasted material.
I used this calculator with the column dimensions and got 17 litres per column, or 68 litres total. At roughly 10 litres per 20 kg bag of concrete mix, that came to 7 bags. I bought 8 as a buffer, which is consistent with what the American Concrete Institute recommends for hand-mixed pours where slump variation is harder to control. I used 7.5 bags and had half a bag of waste. All four footings passed the 48-hour cure check with no cracking.