Concrete Calculator with Cement Bags and Rebar Weight
Work out the concrete volume for slabs, footings, columns, beams and stairs, the cement, sand, gravel and water for your mix, and the weight of reinforcing steel with a 12 m bar cut list. Modelling the structure in Revit? Browse our Revit families.
Slabs, footings, columns, beams, stairsCement bags, sand, gravel, waterCommon site mixes and 1:2:4 ratiosRebar weight d²/162 and exact12 m bar cut list
Elements
For beams, enter the depth below the slab so the slab volume is not counted twice. The stair flight is approximate: steps plus an inclined waist slab; add landings as slabs.
Mix and waste
Quantities per m³ of finished concrete. The first three are cement-content mixes with 0.4 m³ sand and 0.8 m³ gravel per m³, common for site-mixed concrete; your structural engineer's specification and the local code take precedence.
Added to the net volume. 5 % is a common allowance.
Litres of water per kg of cement.
Loose bulk densities for tonnes
Typical values; ask your supplier for the real figure. Used only to convert m³ to tonnes.
Reinforcement
Length is the cut length of one bar, including hooks and bends. Bars longer than the stock length are lapped automatically.
At each end and edge.
Stock bars and laps
12 m is a common mill length; use your supplier's length.
Only used where a bar is longer than the stock length. Take the value from your drawings.
Prices (optional)
Type today's prices from your supplier to get a cost estimate. Leave a field empty to skip it.
Concrete volume
Enter your elements to see the result.
Estimate only. Quantities are for ordering and budgeting, not for design. Mix proportions, cover, laps and bar schedules must come from your structural engineer's drawings and the code that applies to your project, such as ACI 318 or Eurocode 2. Allow extra for spacers, chairs, tie wire and site losses.
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Request a projectEstimate concrete and steel in three steps
Add your elements
Pick slab, footing, column, beam, strip footing, stair flight or a custom volume, type the dimensions in metres or feet and how many there are.
Choose the mix
Use a cement-content site mix (250, 300 or 350 kg cement with 0.4 m³ sand and 0.8 m³ gravel), a nominal ratio such as 1:2:4, or your own quantities, and set the waste allowance and truck size.
Add the rebar
Switch to Rebar weight and list your bars, or describe a slab or footing mesh by spacing and cover. You get kilograms, tonnes, the 12 m bars to buy and a cost if you type prices.
How much cement, sand and gravel per cubic metre
Site mixes are often written as kilograms of cement per cubic metre with 0.4 m³ of sand and 0.8 m³ of gravel (زلط or crushed stone). For a nominal volume mix such as 1:2:4, multiply the wet volume by 1.54 to get the dry volume of materials, split it by the ratio parts, and convert cement at 1,440 kg/m³.
Worked example: a 5 × 4 m slab, 0.15 m thick, is 3 m³. At 350 kg/m³ that needs 1,050 kg of cement, which is 21 bags of 50 kg, plus 1.2 m³ of sand, 2.4 m³ of gravel and 525 litres of water at a water/cement ratio of 0.5.
| Mix (per m³) | Cement | 50 kg bags | Sand | Gravel |
|---|---|---|---|---|
| Plain concrete | 250 kg | 5 | 0.40 m³ | 0.80 m³ |
| Foundations | 300 kg | 6 | 0.40 m³ | 0.80 m³ |
| Reinforced concrete | 350 kg | 7 | 0.40 m³ | 0.80 m³ |
| 1:3:6 | 222 kg | 4.4 | 0.46 m³ | 0.92 m³ |
| 1:2:4 | 317 kg | 6.3 | 0.44 m³ | 0.88 m³ |
| 1:1.5:3 | 403 kg | 8.1 | 0.42 m³ | 0.84 m³ |
The first three rows are common site practice, not values quoted from a code. Codes set minimum cement contents by exposure condition, so always follow your structural specification.
Rebar weight per metre and per 12 m bar
| Bar | kg/m (exact) | kg/m (d²/162) | kg per 12 m bar | 12 m bars per tonne |
|---|---|---|---|---|
| Ø6 | 0.222 | 0.222 | 2.66 | 375 |
| Ø8 | 0.395 | 0.395 | 4.74 | 211 |
| Ø10 | 0.617 | 0.617 | 7.40 | 135 |
| Ø12 | 0.888 | 0.889 | 10.65 | 93 |
| Ø14 | 1.208 | 1.210 | 14.50 | 68 |
| Ø16 | 1.578 | 1.580 | 18.94 | 52 |
| Ø18 | 1.998 | 2.000 | 23.97 | 41 |
| Ø20 | 2.466 | 2.469 | 29.59 | 33 |
| Ø22 | 2.984 | 2.988 | 35.81 | 27 |
| Ø25 | 3.853 | 3.858 | 46.24 | 21 |
| Ø28 | 4.834 | 4.840 | 58.00 | 17 |
| Ø32 | 6.313 | 6.321 | 75.76 | 13 |
The exact value uses a steel density of 7,850 kg/m³. The d²/162 rule is about 0.1 % heavier and is accurate enough for site estimates. Bars per tonne are rounded down.
Add laps where bars are longer than 12 m (often 40 to 50 bar diameters; take the value from your drawings) and allow extra for chairs, spacers and tie wire.
Concrete and rebar questions
It depends on the mix. A typical reinforced site mix of 350 kg/m³ needs 7 bags of 50 kg, plain concrete at 250 kg/m³ needs 5 bags, and a nominal 1:2:4 mix needs about 6.3 bags (317 kg). Round up to whole bags and add a waste allowance, usually around 5 %.
Multiply length × width × thickness, all in metres, to get cubic metres. A 5 × 4 m slab that is 15 cm thick is 5 × 4 × 0.15 = 3 m³. Add about 5 % for waste and spillage before you order ready-mix.
The numbers are parts of cement, sand and coarse aggregate by volume. Because dry materials shrink when mixed with water, you need about 1.54 m³ of dry material per 1 m³ of concrete. For 1:2:4 that gives 0.22 m³ of cement (317 kg), 0.44 m³ of sand and 0.88 m³ of gravel; for 1:1.5:3 it gives 403 kg of cement, 0.42 m³ of sand and 0.84 m³ of gravel.
Weight in kg per metre is the bar diameter in millimetres squared divided by 162. A Ø12 bar weighs 144 ÷ 162 ≈ 0.888 kg/m, so a 12 m bar weighs about 10.7 kg. Multiply by the total length of each diameter, including laps, to get the total weight.
Divide 1,000 kg by the weight of one bar. For Ø12 that is 1,000 ÷ 10.65 ≈ 93 bars, for Ø16 about 52 bars and for Ø10 about 135 bars. The calculator also packs your actual cut lengths into 12 m bars so you can see the offcuts.
List every element: footings, strip footings, columns, beams (depth below the slab only), slabs and stairs. Work out each volume and multiply by the number of identical elements, then add the waste allowance. Enter them as rows in the calculator to get the total in m³, the materials and the number of ready-mix trucks.
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