Key Takeaways
- This tool is built for scenario planning, not one-time guessing.
- Use real baseline inputs before testing optimization scenarios.
- Interpret outputs together to make stronger decisions.
- Recalculate after meaningful context changes.
- Consistency and execution quality usually beat aggressive one-off plans.
What This Calculator Measures
Estimate sample size needed to detect a lift between baseline and target conversion rates.
By combining practical inputs into a structured model, this calculator helps you move from vague estimation to clear planning actions you can execute consistently.
This calculator estimates sample size needed to detect a conversion lift with chosen confidence and power.
How the Calculator Works
n = (zα + zβ)^2 × p(1-p) / Δ^2Target rate: baseline × (1 + lift).
Total sample: per-variant × 2.
Daily traffic: total ÷ duration.
Worked Example
- 3.5% baseline with 15% lift targets 4.0%.
- Confidence and power drive sample size.
- Daily traffic estimate sets feasibility.
How to Interpret Your Results
| Result Band | Typical Meaning | Recommended Action |
|---|---|---|
| Under 5k | Small test. | Feasible quickly. |
| 5k–20k | Moderate test. | Plan for traffic needs. |
| 20k–50k | Large test. | Ensure enough duration. |
| 50k+ | Very large. | Consider bigger lift or longer test. |
How to Use This Well
- Enter baseline rate and target lift.
- Select confidence and power.
- Choose traffic split.
- Set desired test duration.
- Review sample size and daily traffic.
Optimization Playbook
- Target larger lifts: reduces required sample.
- Adjust power: 80% reduces sample size.
- Extend duration: lowers daily traffic needed.
- Keep splits even: minimizes total sample.
Scenario Planning Playbook
- Baseline: current rate and lift.
- Bigger lift: raise lift to 20%.
- Lower power: drop to 80%.
- Decision rule: keep daily traffic achievable.
Common Mistakes to Avoid
- Overestimating lift.
- Ignoring power requirements.
- Setting unrealistic test duration.
- Using uneven traffic splits without planning.
Implementation Checklist
- Confirm baseline conversion rate.
- Choose realistic lift target.
- Set confidence and power.
- Plan traffic needs.
Measurement Notes
Treat this calculator as a directional planning instrument. Output quality improves when your inputs are anchored to recent real data instead of one-off assumptions.
Run multiple scenarios, document what changed, and keep the decision tied to trends, not a single result snapshot.
FAQ
Why does lift affect sample size?
Smaller lifts require more data to detect.
What power should I use?
80% is common, 90% for more confidence.
Can I use uneven splits?
Yes, but it increases total sample requirements.
Related Calculators
- Effect Size Power Planner Calculator
- Confidence Band Width Calculator
- Margin of Error Planner Calculator
Frequently Asked Questions
How accurate are the results?
The Sample Size Lift applies a standard formula to your inputs — accuracy depends on how precisely you measure those inputs. For planning and estimation, results are reliable. For high-stakes or professional decisions, cross-check the output with a domain expert or primary source.
How does the Sample Size Lift Calculator work?
The Sample Size Lift Calculator takes your input values, applies the relevant formula, and returns the calculated result instantly. Each field on the page corresponds to a variable in the underlying equation. You can adjust any input and the result updates automatically, making it straightforward to explore different scenarios and understand how each variable affects the outcome. No sign-up or installation is required — the calculator runs entirely in your browser.
What sample size do I need for reliable results?
It depends on the desired confidence level, margin of error, and population variance. For a typical survey (95% confidence, ±5% margin), n ≈ 385 for a large population. Smaller samples are fine for exploratory analysis, but don't over-interpret the results — widen your confidence intervals to reflect the uncertainty.
Common Tip Percentages
| Service | Typical Tip Range | Notes |
|---|---|---|
| Restaurant (sit-down) | 15–20% | 20%+ for exceptional service |
| Food delivery | 10–20% | Consider extra for long distances |
| Taxi / rideshare | 10–20% | More for assistance with luggage |
| Hotel housekeeping | $2–5/night | Leave daily, not just at checkout |
| Barber / hair salon | 15–20% | On pre-discount total |
| Pizza delivery | 10–15% or $3–5 minimum | Higher in bad weather |
General Household Budget Ratios (50/30/20 Rule)
| Category | % of Net Income | Examples |
|---|---|---|
| Needs | 50% | Rent, groceries, utilities, insurance |
| Wants | 30% | Dining out, entertainment, hobbies |
| Savings / Debt | 20% | Emergency fund, retirement, extra payments |
Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |