Enter the unit load of the test sample and the unit load of the standard sample into the calculator to determine the CBR ratio.

California Bearing Ratio Calculator

Use the main CBR test tab to calculate CBR at 2.5 mm and 5.0 mm, then identify the design value people usually want.

CBR Test
Single Penetration
Main CBR test calculator

Enter corrected test loads at 2.5 mm and 5.0 mm. This calculates both CBR values and shows the design choice rule.

Standard loads used:
2.5 mm = 3020.33 lbf = 13.44 kN = 1370 kgf
5.0 mm = 4530.50 lbf = 20.15 kN = 2055 kgf
Unit
lbf
kN
kgf
Unit
lbf
kN
kgf

This tab is now the main experience because most searchers want the actual CBR test calculation, not a generic ratio solver.

Optional reference context
Sample condition
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Material reference
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CBR Ratio Formula

The following formula is used to calculate the CBR ratio for a given unit load of a test sample and a standard sample. 

CBR = (U_t / U_s) * 100

Variables:

  • CBR is the California Bearing Ratio (%)
  • U_t is the unit load of the test sample
  • U_s is the unit load of the standard sample

To calculate the CBR ratio, divide the unit load of the test sample by the unit load of the standard sample and multiply the result by 100 to get the percentage.

What is a CBR Ratio?

The California Bearing Ratio (CBR) is a penetration test for evaluating the mechanical strength of natural ground, subgrades, and base courses beneath new carriageway construction. The test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area. The CBR value is expressed as a percentage of the actual load causing the penetration to the standard load. This ratio is used to determine the thickness of materials needed for the construction of roads and pavements.

How to Calculate CBR Ratio?

The following steps outline how to calculate the CBR Ratio.

  1. First, determine the unit load of the test sample (U_t).
  2. Next, determine the unit load of the standard sample (U_s).
  3. Next, calculate the CBR ratio using the formula CBR = (U_t / U_s) * 100.
  4. Finally, calculate the CBR Ratio.
  5. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Unit load of the test sample (U_t) = 1500

Unit load of the standard sample (U_s) = 2000