Concrete Calculator Widget
Embed a concrete calculator on a builders' merchant, ready-mix or DIY page. Visitors pick a slab, round column or set of steps, enter the sizes and see the cubic metres or cubic yards to order, the number of pre-mix bags, and - for site mixing - the cement bags, sand and aggregate for a nominal mix.
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<iframe src="https://a2z.tools/embed/w/concrete-calculator" title="Concrete Calculator by A2Z Tools" width="100%" height="900" style="border:0;width:100%" loading="lazy" allow="clipboard-write"></iframe>
A plain iframe. Works everywhere, including site builders that strip scripts. Adjust height if your content needs more room.
<div data-a2z-widget="concrete-calculator" data-height="900"></div> <script async src="https://a2z.tools/embed.js"></script>
Adds a small script (what it does) that sizes the widget to fit its content, loads it lazily and keeps it isolated from your page's CSS.
Works with
How it works
The volume of one piece is length x width x thickness for a slab, footing or wall, pi x radius² x height for a round column or sonotube, and width x tread x rise x n(n+1)/2 for n solid steps cast on the ground (each step is a block as tall as all the steps up to it). That is multiplied by the number of identical pieces and increased by the waste allowance. Pre-mix bag counts use the manufacturer's yields - 0.60 cu ft from an 80 lb bag, 0.45 from 60 lb and 0.30 from 40 lb - and metric 25 kg and 40 kg bags are scaled by weight from the same yield, about 11.7 litres per 25 kg. For site-mixed concrete, a nominal ratio such as 1:1.5:3 is applied to the dry volume, 1.54 times the wet volume, with cement at 1,440 kg/m³ in 50 kg bags: 1 m³ of 1:1.5:3 needs 8.06 bags of cement, 0.42 m³ of sand and 0.84 m³ of coarse aggregate.
Calculation method
- Slab, footing or wall: V = length x width x thickness
- Round column: V = pi x (diameter / 2)^2 x height
- Solid steps on grade: V = width x tread x rise x n(n + 1) / 2 for n steps
- Order volume = V x pieces x (1 + waste / 100); 1 yd3 = 27 cu ft = 0.764555 m3
- Pre-mix bags = ceil(order volume / bag yield); yields 0.60, 0.45, 0.30 cu ft for 80, 60, 40 lb; metric bags scaled by weight (0.0117 m3 per 25 kg)
- Site mix a:b:c: dry volume = 1.54 x wet volume; cement = dry x a / (a + b + c) x 1440 kg/m3 / 50 kg per bag; sand = dry x b / sum; aggregate = dry x c / sum
Worked examples
Shed base in feet
Inputs: Slab 10 x 10 ft, 4 in thick, 0% waste, 80 lb bags
Result: 1.23 yd³ (33.3 cu ft); 56 bags
10 x 10 x 4/12 = 33.33 cu ft; / 27 = 1.235 yd³; 33.33 / 0.60 = 55.6, rounded up to 56.
Site-mixed M20 slab
Inputs: 3 x 3 m, 10 cm thick, 0% waste, 1:1.5:3
Result: 0.9 m³; 7.3 bags of cement; 0.378 m³ sand; 0.756 m³ aggregate
Dry volume 0.9 x 1.54 = 1.386 m³; cement 1.386 / 5.5 = 0.252 m³ x 1440 = 362.9 kg = 7.26 bags.
Four round piers
Inputs: Column 30 cm diameter, 3 m high, 4 pieces, 0% waste
Result: 0.848 m³
pi x 0.15² x 3 = 0.2121 m³ per pier x 4.
A quantity estimate for planning, not a structural or mix design.
Limitations
- Volumes assume square, level forms; a sub-base that dips or a form that bows adds concrete the widget cannot see.
- Metric bag yields are scaled from a US manufacturer's figures by weight; check the yield printed on the bag you buy.
- The 1.54 dry-volume factor and the nominal ratios are customary site practice, not a designed mix; structural concrete should follow the engineer's mix design and a standard such as IS 456 or ACI 318.
- Steps are modelled as solid on the ground; suspended stairs with a waist slab need a different calculation.
Where publishers use it
- Ready-mix suppliers' order pages, so customers know the cubic yards before they call
- Hardware stores listing bagged concrete next to the bag-count result
- Patio, shed-base and driveway how-to guides
- Indian and South-Asian building blogs that quote cement bags for M15 and M20 work
- Fence and deck installers explaining post-hole and pier concrete
Questions
How many bags of concrete for a 10 x 10 ft slab 4 in thick?
The slab is 33.33 cu ft, or 1.23 cubic yards. At 0.60 cu ft per 80 lb bag that is 55.6, so 56 bags before waste - at that size a ready-mix truck is usually simpler and cheaper.
How many cement bags are in 1 m³ of M20 concrete?
With the nominal 1:1.5:3 mix and a dry-volume factor of 1.54, the cement is 1.54 / 5.5 = 0.28 m³, or 403 kg - 8.06 bags of 50 kg - with 0.42 m³ of sand and 0.84 m³ of coarse aggregate. A designed mix from a lab can use a different amount.
Why multiply by 1.54 for dry materials?
Loose cement, sand and stone contain air, and the sand bulks when damp, so about 54% more dry material is needed than the finished volume of compacted concrete. It is a long-standing site rule of thumb for nominal mixes, not a property of a particular mix.
How much waste should I add?
5% for formed slabs on level, compacted ground, and up to 10% where the sub-base is uneven, the pour is small or the concrete is placed by hand. Running short mid-pour leaves a cold joint, so it is cheaper to have a little left over.
How do I work out concrete for round posts?
Choose Round column and enter the hole diameter and depth, then the number of holes. A 30 cm hole 3 m deep holds 0.212 m³; four of them need 0.848 m³ before waste. Subtract the post itself if a timber post is set in the hole.
How is the volume of steps calculated?
Each step is a block from the ground to its own tread, so for n steps the total is width x tread x rise x (1 + 2 + ... + n). Three 1 m wide steps with 18 cm rises and 28 cm treads hold 1 x 0.28 x 0.18 x 6 = 0.302 m³.
Sources
- Concrete Mix Product No. 1101 data sheet - QUIKRETE . A 40 lb bag yields approximately 0.30 cu ft, 60 lb 0.45 cu ft and 80 lb 0.60 cu ft (8.5, 12.7 and 17 L). The 1.54 dry-volume factor is a site convention with no code source and is labelled as such.
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Concrete Calculator by A2Z Tools - https://a2z.tools/embed/concrete-calculator
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