Sample Size Formula

n = z² * p * (1 - p) / e²

Where,

z value (e.g. 1.96 for 95% confidence level)

p = proportion (as a decimal),

e = margin of error (%).

Sample Size (with finite Population Correction)

n = [z² * p * (1 - p) / e²] / [1 + (z² * p * (1 - p) / e² * N)]

Where,

z value (e.g. 1.96 for 95% confidence level)

p = proportion (decimal),

N = population size,

e = margin of error.

Population Size - The total number of people whose opinion or behaviour your sample will represent.

Confidence Level (%) - The Probability that your sample accurately reflects the attitudes of your population.The industry standard is 95%.

Margin of Error (%) - The range (measured as a percentage) that your populations response may deviate from your samples.

z value

Our calculator used the following z-score values.