How many responses before you can trust the number?
Before you commission a survey, know how many completed responses the decision needs. Enter confidence, margin of error and population; get the sample size — and a clear statement of when the formula does not apply.
Standard simple-random-sample formula: n = Z² × p(1−p) ÷ e², with finite-population correction when the population is known. At 95% confidence, ±5% margin, p=50%: n = 385.
p = 50% is the conservative default because it maximizes required sample. If prior evidence suggests a skewed proportion, the required n falls.
Critical honesty: opt-in panels and convenience samples do not inherit this margin of error. Weighting and design effects increase requirements. The tool says so on the output.
Illustrative figures, not a client outcome.
You can — the margin of error widens. At n=100 the margin is roughly ±10%. For directional reads between very different options, that may be enough; for pricing decisions, it rarely is.
Not statistically. Opt-in dealer polls are valuable qualitative signal, but they are not a probability sample — read them as direction, not measurement.
Version 1.0 · Reviewed 2026-10 · Methodology is fixed and version-controlled; results depend on your inputs.
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