Stratified Sample Size Calculator

Work out stratified sample size instantly with clear inputs, formula shown and shareable results.

About Stratified Sample Size Calculator

Proportional stratified allocation gives each stratum a share of the sample matching its share of the population: nₕ = n·Nₕ/N. This guarantees representativeness and usually reduces variance relative to simple random sampling.

Formula

Proportional allocation

nₕ = n · Nₕ / N

Worked example

With the default values below, Stratified Sample Size Calculator returns Proportional allocation per stratum of 80, 120, 200. Change any input above and every figure here is recalculated in your browser.

Inputs used

Population size of each stratum: 2000, 3000, 5000
Total sample sizeminimum 1: 400

Results

Proportional allocation per stratum: 80, 120, 200
Sample from the largest stratum: 200.0000
Total population: 10,000
Equal allocation for comparison: 133.3333

Step by step

1Values used
2Proportional allocation
3Proportional allocation per stratum= 80, 120, 200
4Sample from the largest stratum= 200.0000
5Total population= 10,000
6Equal allocation for comparison= 133.3333

Assumptions and limits

The result is derived only from the 2 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

For strata of 2000, 3000 and 5000 with a sample of 400?

The allocation is 80, 120 and 200 — proportional to the 20%, 30% and 50% shares.

When is equal allocation better?

When you need comparable precision within each stratum, such as comparing small subgroups against large ones.