Concrete Mix on Site

Use this calculator to determine how much sand, aggregate (gravel) and cement is required for mixing on site a given area of concrete (1:2:4 ratio).

We also have a 'Imperial' version of this calculator here.


Length in Metres
Width in Metres
Desired compacted depth in mm
Total m3


      25 Kg bags 40 Kg bags 1 tonne bags
Cement Kg
Sharp Sand Kg
Aggregate Kg
Water litres  


Ballast (all in) tonnes      
Ballast (all in) m3      

Desirable properties in a concrete mix

  • Ensure the concrete mix is workable which allows correct placement and consolidation
  • Ensure the optimum desired quality of the hardened concrete is met which improves resistance to freezing and thawing, water tightness (low permeability) , wear resistance, and strength
  • The quality of the concrete is dependant mainly on the water to cement ratio, so water requirements should be minimised to reduce the cement requirement thereby reducing the overall cost
  • The mix should be a stiff as possible
  • Use the largest aggregate practicable
  • Use the optimum ratio of fines to coarse aggregate
  • A low water to cement ratio is the number one issue that affects concrete quality. Do not add too much water

Components in concrete

  • Portland Cement - the aggregate and sand is coated by a paste formed from the cement and water. This paste then hardens and binds the fines (sand) and aggregate together
  • Water - this is needed to chemically react with the cement and to make the concrete workable
  • Aggregate - The fines are sand and gravel or crushed stone is the coarse aggregate (10, 20 & 40mm) in most mixes

Admixtures in Concrete

  • Accelerators - added to the concrete to reduce overall setting times and gain early strength. Calcium chloride is the lower cost accelerator, however a non-chloride accelerator should be specified if reinforcing has been used, to prevent corrosion of the steel
  • Retarder - used in hot weather to delay setting. Also used for difficult jobs and specialist finishes. May also act as a water reducer
  • Fly Ash - improves workability, easier to finish and reduces the cement content
  • Air Entrainment - improves the workability of the concrete as well as the durability