Use transferred bytes, not source-file size
Measure a representative page load after compression. Include first-party images, fonts, scripts and API responses billed to the service you are estimating. Third-party resources may be billed elsewhere. Return visits and cached assets can reduce transferred bytes; use an average appropriate to your visitors rather than assuming every view is a cold load.
Other outbound transfer covers downloads, API traffic or backup exports not already included in page weight. Avoid counting those bytes twice. Monthly page views are a scenario input, not predicted traffic.
Billing limits
The model uses decimal units: 1 GB = 1,000 MB. A provider that bills GiB uses a different unit; convert its allowance and price before entering them. One flat overage rate is applied above the allowance. Tiered prices, destination-specific charges, request charges, minimum fees and taxes are excluded.
An allowance of zero means all transfer is chargeable; no percentage-used figure is then shown. Compare the estimate with official network pricing and your own invoice. Add recurring costs to the hosting comparison, or estimate the time for one transfer with download and upload time.