ClarivoxxBy Abdessamad Ghanem

Free tool

Survey Sample Size Calculator

Sample size n = z² × p(1 − p) ÷ e², then corrected for your population: n ÷ (1 + (n − 1) ÷ N). With 5,000 customers, 95% confidence and a 5% margin of error you need 357 responses. Divide by your response rate to know how many customers to invite.

Responses needed

357

With 357 answers, the true score is within ±5% of your result 95% of the time.

Customers to invite

1,785

Without population limit

385

n₀ = z² × 0.25 ÷ e² = 1.960² × 0.25 ÷ 0.050² = 385
n = n₀ ÷ (1 + (n₀ − 1) ÷ 5,000) = 357

Frequently asked questions

How many survey responses do I need?
For 95% confidence and a ±5% margin of error, about 385 responses is enough for any large population, and fewer for small ones: 357 for 5,000 customers, 218 for 500. If you want ±3%, you need roughly three times as many.
What confidence level and margin of error should I use?
95% confidence with a ±5% margin is the usual default for customer surveys. Use ±3% when you compare segments or track small changes over time, and accept ±10% for quick internal pulse checks.
Does the response rate change the sample size?
No, it changes how many people you must invite. If you need 357 responses and 20% of customers usually answer, invite about 1,785. Also check that those who answer look like your whole customer base.

About the author

Abdessamad Ghanem

Customer Experience & Customer Success Consultant · Founder of Clarivoxx

Abdessamad Ghanem works across Customer Support, Sales, Customer Success, Account Management and Partner Management. He writes Clarivoxx Insights for B2B SaaS professionals who own retention, adoption and customer outcomes.

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