Effective Population Size Tools

Created By : Bhagya
Reviewed By : Rajashekhar Valipishetty
Last Updated at : Apr 18,2023

Effective Population Size Tools helps you to compute effective population size using the sex-ratio equation. So, enter the input values in the below box and click the calculate button provided next to the input to get the outcome in a short time span.

Choose a Calculation:
Number of males(Nm):
Number of females(Nf):

Effective Population Size Tools: Effective Population Size Tools is a concept useful in the determination of population size in association with the sex ratio. Do you think finding Effective Population Size is tough and complicated? Not anymore, because we have come up with the Effective Population Size Tools that saves your useful time and gives output with detailed explanation fastly. We have also enclosed some solved examples for a better interpretation.

What is Effective Population Size?

Effective Population is the size of the ideal breeding population out of the total census population. Basically, it is the number of breeding populations (it should include the number of males & females who are fertile). It is denoted as ‘Ne’.

The census population is always smaller than the effective population size. In very rare cases, the census population is equal to the effective population, provided all the members in the population should be fertile & should have an equal number of male & female numbers.

Genetic Variation: Importance

Genetic variety is crucial because it increases the chances of a species' survival. When populations become smaller and isolated, genetic diversity is lost, reducing a species' ability to adapt and thrive.

Effective Population Size Formula

The Gender-Ratio Equation or formula which is required for determining the effective population size is:

Ne = 4 × Nf × Nm / (Nf + Nm)

Here, Nf & Nm = the respective no of females and males within a given population.

P = census count

If male & female population is equal, then

Nf = Nm = P/2

Then in this case, the effective population size is given by:

Ne = 4 (P/2) (P/2) / (P/2 + P/2) = P2 / P = P

It implies that, in the case of an equal population of males & females, census count & effective population size are equal. In actual terms, in the presence of an alternative gender ratio, the effective size is less than the count of the census.

Impact of gender ratio on effective population size

The Gender ratio directly impacts the effective population size. Gender ratios are one of the most basic demographic indicators, indicating both the relative longevity of females and males as well as a population's future reproductive potential.

The distortion in the gender ratio leads to the reduction in the effective population size, which reduces the effectiveness of natural selection and leads to higher rates of changes in the genetics of the population (genetic drift), inbreeding, and loss of genetic variation.

How to Calculate the Effective Population Size?

We can use the formula mentioned above to calculate the effective population size. Census & effective population are equal only if there are equal no of fertile males & females in given population. The steps to calculate the effective population are mentioned below:

  1. Consider the population of a particular region.
  2. Now, figure out the total number of males(Nm) & females(Nf) in the population.
  3. By using the male and female count apply the Gender-Ratio Equation which is required for calculating the effective population size.
  4. Use the effective population size formula for calculating the effective population immediately.

Ne = 4 × Nf × Nm / (Nf + Nm)

  1. Finally, the calculated value is the Effective Population size.
  2. Determine the Census count P.
  3. Compare the effective population size with the census count to check whether both values are equal.

Individuals of any mathematical knowledge can now compute the lengthy calculations, and understand tough concepts easily taking the help of our calculators at arithmeticcalculator.com.

Solved Effective Population Size Example


If the male population is 100 & female population is 124. Then calculate the effective population size.


Here, Nf = 124 & Nm = 100

Using the formula:

Ne = 4 ( Nf × Nm ) / (Nf + Nm)

= 4 (124 × 100) / (224) = 221.42

Approximate value of effective population is 222.

Here, we will calculate census population by adding both the values (Nf + Nm).

So, census population = 224

We can say that ‘effective population size’ is less than ‘census population size’.

FAQs on Free Online Effective Population Size Tools

1. What is the effective population size of humans?

Approximately 65,000 years ago studies have evaluated the conventional effective population size at 12,800 to 14,400.

2. What is effective population size in ecology?

It is considered the most important parameter in ecology. Effective population size is beneficial in translating the census size of an actual population into the size of a hypothetical population depicting an equal rate of loss of genetic diversity similar to the real population under analysis.

3. What factors affect effective population size?

Some of the factors that affect the effective population size are, number of parents, average number of offspring per family and family size.

4. What would increase the effective size of a population?

The sex ratio of the breeding animals effects on the increase of an effective population size.