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.
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Hole Volume Calculator Logic
Frequently Asked Questions
Muhammad Shahbaz Siddiqui
Founder, TheCalculatorsHub
How I worked out how much concrete to pour per post hole
I was setting 16 fence posts around my property. Each hole was 200 mm in diameter and 750 mm deep, dug with a post-hole auger. Before calculating how many bags of ready-mix to buy, I needed the total concrete volume across all 16 holes.
This calculator gave me 3.77 litres per hole and 60.3 litres total. At 10 litres per 20 kg bag, that came to 6 bags with a small buffer. According to the ACI's guidance on post-setting concrete, the recommended practice is to crown the concrete slightly above grade to shed water, which adds about 5-8% to the volume. I bought 7 bags, set all 16 posts in a single day, and had half a bag left over. The fence line is still perfectly plumb 6 months later.