A/B Testing Bandwidth Cost Formula
Learn how to estimate the monthly CDN or hosting bandwidth cost added by an A/B test payload.
This calculation estimates the incremental data transfer created when an experiment sends extra code, content, images, or other assets to a share of eligible page views. It helps isolate experiment delivery cost from the normal bandwidth required to serve the website.
- 100% Free
- No Sign-Up Required
- Private & Secure
- Mobile Friendly
Estimated Monthly A/B Test Bandwidth Cost
Where:
Estimate eligible page views, apply the percentage included in the test, multiply by the extra payload on each exposure, convert KB to decimal GB, and multiply by the provider's price per GB.
Variables Explained
| Variable | What It Means | Unit |
|---|---|---|
| monthlyVisitors - Monthly visitors | Estimated unique visitors during one month. | visitors |
| pageviewsPerVisitor - Average page views per visitor | Average number of eligible page views generated by each visitor. | page views |
| trafficAllocation - Test traffic allocation | Percentage of eligible page views that receive the experiment payload. | percent |
| additionalPayloadKb - Additional test payload per page view | Extra data delivered because of the test on each exposure. | KB |
| cdnCostPerGb - Bandwidth cost per GB | Your CDN, hosting, or delivery provider's charge for one GB of data transfer. | currency |
Step-by-Step Calculation
Estimate eligible page views
Multiply monthly visitors by average eligible page views per visitor.
eligiblePageviews = monthlyVisitors * pageviewsPerVisitor
Calculate test exposures
Apply the experiment allocation to estimate how many page views receive the extra payload.
testPageviews = eligiblePageviews * (trafficAllocation / 100)
Calculate extra transferred data
Multiply test exposures by the additional payload delivered per exposure.
additionalDataKb = testPageviews * additionalPayloadKb
Convert kilobytes to gigabytes
The calculator uses decimal bandwidth units: 1 GB equals 1,000,000 KB.
additionalBandwidthGb = additionalDataKb / 1000000
Estimate monthly cost
Multiply incremental bandwidth by the stated delivery price per GB.
monthlyBandwidthCost = additionalBandwidthGb * cdnCostPerGb
Annualize the estimate
Multiply the monthly estimate by 12 when traffic, allocation, payload size, and pricing remain stable.
annualBandwidthCost = monthlyBandwidthCost * 12
Example: 100,000 monthly visitors and a 50% test
Eligible page views
100,000 × 4
400,000 page views
Test exposures
400,000 × (50 ÷ 100)
200,000 exposures
Additional data
200,000 × 150 KB
30,000,000 KB
Additional bandwidth
30,000,000 ÷ 1,000,000
30 GB
Monthly bandwidth cost
30 × $0.08
$2.40 per month
Annualized cost
$2.40 × 12
$28.80 per year
Final Result
The experiment adds an estimated 30 GB of monthly transfer and costs about $2.40 per month, or $28.80 annually.
Assumptions
- ✓Only the additional payload caused by the experiment is counted; normal page delivery is excluded.
- ✓Each visitor generates the stated average number of eligible page views.
- ✓The test allocation stays consistent across the month.
- ✓The stated additional payload is transferred on every estimated test exposure.
- ✓Bandwidth is converted using decimal units, where 1 GB equals 1,000,000 KB.
- ✓The per-GB price excludes taxes, minimum commitments, and other provider fees.
Limitations
- !Caching, compression, and conditional asset loading may mean less data is transferred than the estimate.
- !Regional prices, free allowances, tiered rates, and minimum charges can make an invoice differ from a simple per-GB estimate.
- !Visitor behavior on test pages may differ from the site-wide average used in the calculation.
- !A payload reported by a development tool may not equal the bytes billed after network transfer and provider processing.
Common Mistakes to Avoid
Entering the total page weight instead of only the extra bytes caused by the experiment.
Using visitors instead of page views when the payload can load on several pages per visitor.
Forgetting to convert a percentage allocation such as 50% into 0.50 in manual calculations.
Treating KB as GB without dividing by 1,000,000 under the calculator's decimal convention.
Assuming every test asset is newly downloaded even when it is shared or cached.
Using a list price per GB while ignoring a provider's included transfer allowance or tiered billing.
Related Formulas
Frequently Asked Questions
How is A/B testing bandwidth cost calculated?
It is estimated by multiplying monthly visitors, eligible page views per visitor, test allocation, and extra payload size, then converting the result to GB and applying the cost per GB.
What is included in an A/B test payload?
It can include extra experiment JavaScript, variant markup, images, fonts, personalization data, or other assets delivered because of the test.
Does 100% traffic allocation double the cost of a 50% test?
Usually, yes. If behavior and payload delivery are otherwise the same, moving from 50% to 100% allocation doubles estimated test exposures and incremental transfer.
Why does the formula divide by 1,000,000?
It converts kilobytes to decimal gigabytes because 1 GB is treated as 1,000,000 KB in this calculator.
Does this estimate total website bandwidth?
No. It estimates only the extra transfer attributable to the experiment payload, not the full cost of delivering the page.
Ready to calculate your result?
Use the calculator to get instant results with your own inputs.