Sample Size Calculator

B+L Sampling Size Calculator

One of the most important factors in relation to surveys is the question of how many interviews should be carried out. The B+L Sampling Calculator can help give you an idea of what is appropriate. With the help of a little information, you can assess how many interviews you should carry out in a survey:


The sampling error which is acceptable for you indicates how large the acceptable deviation is. A deviation of 5% is generally always acceptable.

Example: You would like to carry out a survey to assess the awareness of a product among project developers.

Sampling errors:If in reality the product is known by 50% of all project developers, then with your chosen level of sampling error, the product awareness measured should be between 45% and 145%.


The confidence level is the certainty which you desire for your analysis. Typical values are: 90%, 95%, 99%.

For example: You advance the hypothesis that your product is more well known in the north than in the south. If this hypothesis is true, then there will be a maximum 95% probability that it will be rejected.

How many individuals or companies can you choose your sample from? For example, if you wish to conduct a satisfaction survey using a random sample from your 2,400 customers, then please enter 2,400 here. If you do not have any idea of the overall survey population, you can leave this field open. A representative number of 20,000 will then be entered here.

Your recommended sample size: