What is the California Bearing Ratio?

California Bearing Ratio (CBR) BS 1377-9 is the definitive measurement for determining the thickness of roads and their load bearing strength. It is commonly used to assist with the designing and construction of roads, pavements, car parks, runways, and foundations. The ratio is measured using a standardised penetration test and was originally developed by the California State Highway Department in 1990.

GSTL maintains two types of California Bearing Ratio Test frames:

  • Vehicle mounted
  • JCB attachment

The California Bearing Ratio Test will be carried out by one of our trained technicians. They will arrange to go to the site using a 4-wheel drive or JBC to provide the force and transport the specialist equipment.

Once set up they will insert a cylindrical plunger into the previously prepared ground at regular intervals. This will measure the pressure needed to penetrate a standard area of soil. The test is repeated up to 10 times and should be completed within a day, for the rapid reporting of results.

Boring for a new soil sample

What projects need a CBR Test?

Roads & Pavements

If your project involves constructing roads or pavements, you will need a California Bearing Ratio Test. The test determines the strength or the load bearing capacity of the highway subbase and subgrade soil. The test is designed to replicate the stresses placed on subgrade soils once they are subjected to vehicular traffic. It will also allow you to select the appropriate pavement thickness.


In civil engineering you must consider the stability, strength, and characteristics of the ground you are building on.

Undertaking a California Bearing Ratio Test is the easiest way to determine if the soil is suitable for your project. It will identify if you need to incorporate additional elements into the design to increase stability of your planned construction.

Please visit our Plate Bearing Test section for testing on working platforms.