Effective Population Size Calculator

Work out effective population size instantly with clear inputs, formula shown and shareable results.

About Effective Population Size Calculator

Applies the unequal sex ratio formula for effective population size and converts it into the rate at which inbreeding accumulates.

Formula

Effective population size

Ne = 4 Nm Nf / (Nm + Nf); inbreeding per generation = 1 / (2 Ne)

Worked example

With the default values below, Effective Population Size Calculator returns Effective population size of 64.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Breeding malesaccepts 1–1,000,000: 20
Breeding femalesaccepts 1–1,000,000: 80
Census population sizeaccepts 1–10,000,000: 400

Results

Effective population size: 64.00
Effective to census size ratio: 0.1600
Inbreeding accumulated per generation: 0.7813%
Effective size as a share of breeders: 0.6400

Step by step

1Values used
2Effective population size
3Effective population size= 64.00
4Effective to census size ratio= 0.1600
5Inbreeding accumulated per generation= 0.7813
6Effective size as a share of breeders= 0.6400

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is Ne usually far below census size?

Unequal sex ratios, variance in reproductive success and fluctuating numbers all reduce it, often to a tenth of the census.

What is the 50/500 rule?

Ne of 50 is the short-term minimum to limit inbreeding and 500 the long-term minimum to retain adaptive variation.