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Feature Flag Exposure Calculator

Work out feature flag exposure instantly with clear inputs, formula shown and shareable results.

About Feature Flag Exposure Calculator

A feature flag serves two purposes that pull in opposite directions: limiting blast radius and measuring effect. The standard approximation for a two-proportion test needs about 16 p(1-p)/delta^2 users per arm, so detecting a 5 percent relative lift on a 4 percent baseline takes roughly 240,000 users — far more than a cautious 10 percent rollout provides.

Formula

Exposure and power

exposed = users x rollout; sample per arm ~ 16 p(1-p) / (p x relative MDE)^2

Worked example

With the default values below, Feature Flag Exposure Calculator returns Users exposed to the flag of 50,000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total usersminimum 1
500,000
Flag rollout percentageaccepts 0.001–100 %
10 %
Baseline conversion rateaccepts 0.001–100 %
4 %
Relative effect to detectaccepts 0.1–100 %
5 %

Results

Users exposed to the flag
50,000
Sample needed per arm
153,600
Power assessment
Insufficient exposure - raise the rollout percentage or accept a larger detectable effect
Rollout percentage needed for the target effect
30.72%

Step by step

  1. 1Values used
  2. 2Exposure and power
  3. 3Users exposed to the flag= 50,000
  4. 4Sample needed per arm= 153,600
  5. 5Power assessment= Insufficient exposure - raise the rollout percentage or accept a larger detectable effect
  6. 6Rollout percentage needed for the target effect= 30.72

Assumptions and limits

  • The result is derived only from the 4 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 2 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

Can I use a small rollout for both safety and measurement?

Rarely. Use a small rollout to verify it does not break, then raise it to a statistically meaningful share to measure the effect.

What happens to flags after the rollout?

They must be removed. Long-lived flags multiply the number of code paths, and each combination is a configuration nobody has tested.

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Feature Flag Exposure Calculator | Calcrivo