Donaldson R F Page Weight & Cache Calculator
Enter how heavy your pages are, how many people visit and how much is cached, then see the monthly data transfer, the cost, and what a lighter, better-cached site would save.
Projection, not a measurement. Every number comes from the assumptions you type. The tool does not load or measure any page. Real traffic also includes bots, video, downloads and CDN behaviour, so use your host's own statistics for anything that matters, and never for billing.
Your site today
The improved version
Cost and connection
The values above are examples only: use your own page weight, visits and your host's price per GB (or 0 if your plan has no transfer charge).
| No caching | Today | Improved |
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The model
Visits = page views ÷ pages per visit. With no caching every page view downloads the full page weight. With caching, the cacheable part of a page (images, styles, scripts and fonts that do not change) is only downloaded when it is not already in the visitor's browser: on the second and later pages of a visit it is fetched only for the share of requests that miss the cache (1 − hit rate), and on the first page of a visit only returning visitors benefit. So a later page weighs weight × (1 − cacheable × hit rate), and the first page of an average visit weighs weight × (1 − returning × cacheable × hit rate). Monthly transfer is the sum over all visits, in GB of 1,000 MB. Cost is (transfer − free allowance) × price per GB, never below zero. Transfer time is the size in megabits divided by the connection speed, without latency or server delays.
Ways to move the numbers: compress and resize images (see the Image Compressor and Image Resizer), minify code (CSS, HTML), and set long cache lifetimes for files that do not change so the hit rate rises. To see how long a file takes to download on a given connection use the Download Time Calculator. The hit rate is the hardest input to know: start with a low guess, and treat the result as a range, not a promise.
Source / Last verified: arithmetic on your own inputs; no external data, prices or carbon figures are used. Checked on 26 September 2026 with a worked example: 2.5 MB pages, 70% cacheable, 80% hit rate, 100,000 views, 3 pages a visit and 30% returning visitors give about 142.7 GB a month, against 250 GB with no caching (a 42.9% saving).