A/B Testing Memory Requirement Formula
Learn how annual and peak A/B testing event storage are estimated from traffic, event volume, record size, retention, and replication.
This calculation estimates how much replicated storage A/B test event data can require over a year and at the end of a chosen retention window. It helps translate expected experiment traffic and tracking detail into capacity-planning figures.
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Annual Replicated A/B Test Storage
Where:
Multiply daily test visitors by events per visitor and the stored size of each event. Convert KB to GiB, multiply by 365 days, then multiply by the number of stored copies.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| V - dailyVisitors | Average number of unique visitors participating in active A/B tests each day. | number |
| E - eventsPerVisitor | Average number of stored A/B testing events generated by each visitor per day. | number |
| S - eventSizeKb | Average stored size of one event record after serialization, filtering, and any compression. | KB |
| R - replicationFactor | Number of copies retained by the storage system. | number |
| D - retentionDays | Number of days of event data kept in the primary retention window. | days |
| N - variants | Total control and treatment variants used to show average daily visitors per variant. | number |
Step-by-Step Calculation
Estimate daily event records
Find the total number of A/B testing records written in an average day.
dailyEventRecords = dailyVisitors * eventsPerVisitor
Convert records to daily data volume
Convert the daily event payload from KB to GiB using 1 GiB = 1,048,576 KB.
dailyDataGb = dailyEventRecords * eventSizeKb / 1048576
Calculate annual raw storage
Project one year of unreplicated event data at the average daily ingestion rate.
annualRawStorageGb = dailyDataGb * 365
Apply replication
Account for each stored copy of the annual event data.
annualStorageGb = annualRawStorageGb * replicationFactor
Calculate peak retained storage
Estimate occupied replicated capacity when the selected retention window is full.
peakRetainedStorageGb = dailyDataGb * retentionDays * replicationFactor
Show traffic per variant
Divide total daily test visitors evenly across variants for a simple traffic-per-variant reference.
averageVisitorsPerVariant = dailyVisitors / variants
Example: Two-variant experiment with 10,000 daily visitors
Daily event records
10,000 × 10
100,000 records/day
Daily raw data volume
100,000 × 2 ÷ 1,048,576
0.1907 GiB/day
Annual raw storage
0.1907 × 365
69.62 GiB/year
Annual replicated storage
69.62 × 2
139.24 GiB/year
Peak retained storage
0.1907 × 365 × 2
139.24 GiB
Average visitors per variant
10,000 ÷ 2
5,000 visitors/day
Final Result
The estimated requirement is 139.24 GiB of replicated A/B test event storage per year, with 139.24 GiB retained at a 365-day retention limit.
Assumptions
- ✓Daily visitor volume remains broadly consistent throughout the year.
- ✓Each participating visitor creates the stated average number of stored events every day.
- ✓The event-size input represents the stored payload after applicable filtering, serialization, and compression.
- ✓Replication is a direct storage multiplier.
- ✓Visitors are split evenly among variants when calculating visitors per variant.
Limitations
- !The calculation excludes indexes, partitions, metadata, query-engine structures, backups, logs, and minimum storage allocations.
- !Traffic spikes, major experiment launches, and changes to instrumentation can raise actual ingestion above the average.
- !Storage platforms may report decimal GB rather than binary GiB.
- !Archiving, deduplication, compaction, and compression behavior can change actual capacity consumption.
Common Mistakes to Avoid
Entering the uncompressed event size when the storage system stores compressed records.
Counting only conversion events and omitting exposures, page views, clicks, or other tracked events.
Using the number of variants as a multiplier for total traffic when visitors are simply divided among variants.
Treating annual generated storage as the same as retained storage when retention is shorter than 365 days.
Forgetting that a replication factor of 2 means two full stored copies.
Leaving out capacity for indexes, backups, and operational headroom.
Related Formulas
Frequently Asked Questions
How is annual A/B testing storage calculated?
Annual replicated storage equals daily visitors multiplied by events per visitor and event size, converted from KB to GiB, then multiplied by 365 and the replication factor.
What is the difference between annual storage and peak retained storage?
Annual storage is the amount generated in a year. Peak retained storage is the amount present at one time after applying the retention period and replication factor.
Do more A/B test variants increase event storage?
Not by themselves when the same total audience is split across variants and event activity per visitor is unchanged. Variants mainly change the traffic available to each group.
Why does the formula divide by 1,048,576?
It converts KB to GiB because one GiB contains 1,048,576 KB under the binary conversion used by this calculator.
Should replication be included in storage planning?
Yes. If a system stores multiple copies for availability or resilience, each copy uses capacity, so replication is included as a multiplier.
Does this formula include database overhead?
No. It estimates event-record payload storage only and does not include indexes, backups, metadata, logs, or platform-specific overhead.
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