Effect Size Calculator

Created By : Vaibhavi Kumari

Reviewed By : Phani Ponnapalli

Last Updated : May 01, 2025

The Effect Size Calculator is a free online application that calculates the effect size for two sets of data values and this tool speeds up the process and provides the results. You may enter the data sets in this calculator, and the effect size, mean, and standard deviation will be determined in a matter of seconds.


Group1
M1(mean)
SD1
Group2
M2(mean)
SD2

Effect Size Calculator: This effect size calculator can be used to quickly and simply calculate the effect size based on the standard deviations and means of two independent groups of the same size. Continue reading further modules to learn what is meant by Effect Size, its Formula, Step by Step Procedure on How to Calculate Effect Size, Worked out Examples on Effect Size, etc.

What is meant by Effect Size and its Formula?

The difference between the mean values of two groups in proportion to standard deviation is referred to as effect size. Regardless of whether research is observational or experimental, effect size may be used to characterize the extent of the disparity. Cohen's d is also known as effect size.

Cohen's d is required in many publications because Cohen's method of assessing the size of an impact, which aids in understanding the difference between two groups, is widely accepted as effective.

The Cohen's d statistic is determined by dividing the difference between two mean values by the population standard deviation, as follows:

Effect Size = (M1 – M2 ) / SDpooled and

SDpooled = √[ (SD12 + SD22) / 2 ]

 

Where,

M1 be the mean of group 1,

M2 is the mean of group 2,

SD1 be the standard deviation of group 1,

SD2 be the standard deviation of group 2,

SDpooled is the pooled standard deviation.

Cohen's d effect sizes should only be used as a guideline. The effect sizes should be evaluated within the context of the research, and information from similar studies/interventions may help with this evaluation.

To convert Cohen's d into a correlation coefficient (r), use the following equation:

r2 = d2 / (4 + d2)

Here, d = Cohen's d effect size.

x̅1 and x̅2 are the means of two data sets.

r is the effect size of the two data sets.

s1 and s2 are the standard deviations of two data sets.

How to use the Effect Size Calculator?

This calculator is used are as follows

  1. Input sample means M1 and M2
  2. Then put the sample standard deviations values for each group 1 and group 2 is denoted as SD1 and SD2.
  3. Click on the calculate button to generate a value for Cohen's d.

Effect Size Examples

1. Find the effect size from the mean values are 4 and 3 and the standard deviations are 2 and 4.

Solution:

Consider the problem, we have

M1 = 4,

M2 = 3,

SD1 = 2,

SD2 = 4

The formula is to calculate the standard deviation is SDpooled = √[ (SD12 + SD22) / 2 ]

SDpooled = √[ (22 + 42) / 2 ] = 3.162

Effect Size = (M1 – M2 ) / SDpooled

 

d = 1.000 / 3.162

d = 0.316

Therefore, the effect size is 0.316.

You can check with the examples for better understanding of the concept and find more similar concepts with the help of this portal called onlinecalculator.guide

FAQs on Online Effect Size Calculator

1. How to calculate the effect size?

  1. Input sample means M1 and M2
  2. Then put the sample standard deviations values for each group 1 and group 2 is denoted as SD1 and SD2.
  3. Click on the calculate button to generate a value for Cohen's d.

2. What is the formula for the pooled standard deviation?

The formula is to calculate the standard deviation is SDpooled = √[ (SD12 + SD22) / 2 ]

3. What is the formula used to calculate the effect size?

The effect size is also known as cohen's d and the formula is Effect Size = (M1 – M2 ) / SDpooled

 

Where,

  • M1 be the mean of group 1,
  • M2 is the mean of group 2,
  • SD1 be the standard deviation of group 1,
  • SD2 be the standard deviation of group 2,
  • SDpooled is the pooled standard deviation.