A/B Testing File Size Calculator FAQ
Answers to common questions about estimating file-transfer impact from A/B test variants, traffic splits, and caching.
This FAQ explains what the calculator estimates, how to choose inputs, and why results may differ from observed transfer data. All results are planning estimates rather than measurements of actual performance or cost.
General calculator questions
Basic questions about the purpose and scope of the calculation.
What does the A/B Testing File Size Calculator estimate?
It estimates total uncached file transfer during an experiment and the difference from serving the control file to all uncached requests.
What is the baseline used for comparison?
The baseline assumes every uncached request during the test receives the control file.
Does the calculator estimate page load time?
No. It estimates data transfer volume only. Loading time also depends on network, rendering, request priority, and other resources.
Can the result be negative?
Yes. A negative result indicates that the variant is smaller and reduces estimated transfer versus the control baseline.
Inputs and setup
How the main calculator inputs affect the estimate.
Should I enter compressed or uncompressed file size?
Use the typical downloaded response size seen by users, such as a compressed transfer size from network tools or delivery analytics.
What counts as a download per visitor?
It is the average number of file requests made by each participating visitor over the test period.
What should I use for variant traffic share?
Enter the percentage of test traffic intended to receive the variant, such as 50 for a balanced test or 10 for a limited rollout.
How should I choose a cache hit rate?
Use a reasonable estimate from comparable delivery data when available; otherwise treat the result as a scenario estimate.
Formula and results
How transfer calculations are constructed and interpreted.
How are uncached requests calculated?
Total requests are multiplied by one minus the cache hit rate expressed as a decimal.
Why are variant requests used in the bandwidth difference?
Control requests match the all-control baseline. The difference comes from requests where the variant replaces the control.
Why does changing the traffic split change total transfer?
A larger variant allocation sends more uncached requests to the differently sized file, increasing its total effect.
What does estimated A/B test transfer include?
It includes the calculated file-transfer volume for both control and variant requests after the assumed cache hit rate is applied.
Accuracy and limitations
Factors that can cause actual transfer to differ from the estimate.
Will the estimate match CDN billing exactly?
Not necessarily. Billing and observed transfer can include headers, retries, other assets, edge behavior, pricing rules, and measurement differences.
Does cache behavior always match the same rate for both variants?
Not always. Different cache keys, headers, URLs, or deployment approaches can produce different cache behavior.
Does a larger file always make the page noticeably slower?
Not necessarily. File size is one factor, while connection speed, compression, prioritization, rendering, and device conditions also matter.
Can I use this for server-side experiments?
It can estimate a file-transfer scenario if the inputs reflect the asset requests and caching behavior of that implementation.
What does a positive A/B test bandwidth difference mean?
It means the selected test allocation is estimated to transfer more data than serving the control file to all uncached requests.
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