Sample Size Calculator and Confidence Interval

Use the online survey calculator to determine your sample size or your confidence interval. The online sample size calculator helps you to exactly define how big your representative statistical sample should be. Knowing the size of the survey sample allows you to accurately estimate the number of people you should involve in your survey.

Sample CalculatorConfidence Interval

Do you need to determine your sample size?

If you need to determine the size of your survey sample, you can use this online calculator. It is a simple and intuitive tool that enables you to know how many respondents you need in your sample. The result is the “representative statistical sample” of your survey. It is called a “sample” because it represents only a part of the total target population that you should involve in your survey.
Learn more about Sample Planning >

Population size
If you don’t know, use 20000
It’s the total number of people that your sample represents and that reflects the true population (if you don’t know, write 20,000 as the sample size don’t change for target populations larger than that and the difference is not statistically significant).
Margin of error
5% is a common choice
It’s the margin of error you can accept (5% is a common true percentage). When the percentage is smaller, you’re closer to the exact answer at a given confidence level. However for lower margin you require a larger sample size.
Confidence level
Typical choices are 90%, 95%, or 99%
It’s the confidence level you can accept expressed as a percentage (90%, 95% and 99% are common levels). It’s the percentage that expresses how confident you are with the results. For example, 95% confidence interval means that 19 times out of 20 the results lies within the margin of error.
Response distribution (%)
Leave 50% if you’re not sure. In most cases this parameter has to be set at 50%.
The results you expect for each question (standard deviation). If you leave 50%, you go with the most conservative assumption.
The number of respondents needed is:
377
Minimum recommended size of your sample.
Alternate scenarios
Sample size
Margin of error
9.78%
6.89%
5.62%
Confidence level
Sample size
267
377
643

Do you need to determine your confidence interval?

The confidence interval is a percentage that describes the confidence level of the result obtained with your survey. If you need to calculate the confidence interval, you can use the online calculator on this page. It is a simple and intuitive tool that enables you to define the confidence interval and to know how much sure you can be of the results obtained from your representative sample.
earn more about the confidence interval >

Confidence level
Typical choices are 90%, 95%, or 99%
It’s the confidence level you can accept expressed as a percentage (90%, 95% and 99% are common levels). It’s the percentage that states how confident you are with the results. For example, 95% means that 19 times out of 20 the results lies within the margin of error.
Sample size
Total number of respondents.
Population size
If you don’t know, use 20000
It’s the total number of people that your sample represents (if you don’t know, write 20,000 as the sample size don’t change for larger populations and the difference is not statistically significant).
Response distribution (%)
Leave 50% if you’re not sure. In most cases this parameter has to be set at 50%.
The results you expect for each question (sample standard deviation). If you leave 50%, you go with the most conservative assumption.
Your confidence interval estimate is:
0

Sample Size Calculator FAQ

What is “sample size,” and why is it important?

The sample size is the number of individuals selected from a larger population to participate in a survey or study. It is important because it ensures that the results are statistically valid and representative of the entire population. A well-calculated sample size reduces the margin of error and increases the reliability of conclusions, making the findings more accurate and applicable.

 

How is the sample size calculated with this calculator?

Our Sample Size Calculator uses four key parameters to determine the optimal sample size:

  • Confidence Level (%): The probability that the sample accurately represents the population. Common values are 95% or 99%.
  • Margin of Error (%): The acceptable level of inaccuracy in the results. A lower margin of error increases accuracy but requires a larger sample size.
  • Population Size: The total number of people that could be included in the study. If the population is small, the calculator adjusts the formula accordingly.
  • Standard Deviation (%): A measure of variability within the population, expressed as a percentage. If the exact value is unknown, a default of 50% (0.5) is often used, as it represents the highest uncertainty and ensures a conservative estimate.

 

By entering these values into the calculator, you will get an accurate estimate of the sample size needed to obtain statistically valid results.

 

What is the difference between a 5% and a 3% margin of error?

The margin of error represents the range within which the survey results may vary from the true population values.

  • A 5% margin of error means that the survey results can fluctuate by ±5% from the actual population values.
  • A 3% margin of error reduces this variability, providing more precise results, but it requires a larger sample size.
  •  

If you need higher accuracy, it is advisable to decrease the margin of error and increase the number of respondents.

 

What happens if the population is very small?

If your population is small (e.g., fewer than 1,000 people), the calculator automatically adjusts the formula to provide a realistic sample size.

For very small populations, you may need to survey a higher percentage of the population to obtain reliable results. In some cases, surveying the entire population (a census) may be more practical than using a sample.

 

Can I use this calculator for any type of research?

Yes! Our Sample Size Calculator is useful for various types of research, including:
• Market research surveys
• Academic and scientific studies
• Social and political research
• Product testing

 

 

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TIM uses IdSurvey data collection software
Dekra trusts IdSurvey for data collection
atos
Aboca uses IdSurvey data collection software
University of Siena trusts IdSurvey for data collection