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Concrete calculator
Cement bags, sand and crush for a slab, beam, column or footing. Enter the size, or the covered area and thickness for a roof slab (lenter).
Result
Enter your sizes to see the result.
How it’s worked out
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How to use this calculator
- Choose how to enter the size: length × width, or covered area for a slab.
- Enter the thickness or height in feet (6 inch slab = 0.5 ft, or type 0'6).
- Enter how many pieces (for example 8 columns of the same size).
- Pick the mix: 1:2:4 for slabs and footings, 1:1.5:3 for columns and beams.
- For a slab, choose the bars and spacing to get the steel weight too.
The formula
Wet volume = length × width × thickness × pieces (or covered area × thickness). Dry volume = wet × 1.54 × (1 + wastage). Each material = dry volume × its part ÷ total parts; for 1:2:4 the total is 7 parts. Cement bags = cement CFT ÷ 1.25.
Slab steel: main bars run along the length at the main spacing, the other bars across. Running feet × kg per foot gives the weight; #4 (½ inch) bar weighs 0.304 kg per foot and #3 (⅜ inch) 0.171 kg per foot.
Frequently asked questions
How many cement bags are needed for a 1,000 sq ft slab?
For a 6 inch slab in 1:2:4: wet volume = 1,000 × 0.5 = 500 CFT, dry = 500 × 1.54 × 1.02 = 785 CFT, cement = 785 ÷ 7 = 112 CFT, about 90 bags.
Why multiply by 1.54 for dry volume?
Sand and crush have gaps that fill with cement paste, so you need about 54% more dry material than the finished wet concrete volume.
Which concrete ratio is used for a roof slab in Pakistan?
1:2:4 is the usual mix for slabs and footings. Columns and beams often use the stronger 1:1.5:3. Lean concrete under floors uses 1:3:6 or 1:4:8.
How much steel goes in a slab?
It depends on bar size and spacing. With #4 bars at 6 inch both ways, a slab needs about 1.3 kg of steel per square foot including laps. Use the slab steel section for your spacing.
Is 1 cement bag 1.25 CFT?
Yes, a 50 kg bag is taken as 1.25 CFT (0.035 m³) on sites in Pakistan.