How the estimate is made
An APK is a ZIP with a fixed structure, so its size is your content after deflate compression plus the runtime that displays it. Text compresses well: HTML and CSS shrink to about a fifth, JavaScript to a third. Images, audio, video and WOFF2 fonts are already compressed and shrink not at all — which is why a 3 MB PNG costs 3 MB in the APK while 3 MB of HTML costs 600 KB. The tool applies those ratios per file type, adds roughly 2.6 MB for the WebView shell and its resources, and 1.2 MB more if push notifications are compiled in. Real builds land within about 10% of the number shown.
Two numbers, two limits
The upload limit — 5 MB free, 18 MB Pro — is measured on your unpacked web content, the number the meter shows. The APK size is what users download and what the Play listing displays; there is no hard limit on it here, but under 10 MB installs noticeably faster and gets fewer abandoned installs. Google Play's own ceiling is 150 MB for the base module, far beyond anything a ZIP-built app reaches.
Where the weight usually is
| Culprit | Typical saving | Fix |
|---|---|---|
| PNG/JPEG photos and screenshots | 60–80% | Convert to WebP at quality 75–82; resize to the largest size the page actually displays |
| Full font families (TTF/OTF) | 80–90% | WOFF2, subset to the weights and characters used; or use system fonts in the app |
| Un-minified or unused JavaScript | 50–70% | Minify; import only what you use; drop libraries that Chrome on Android already covers (polyfills, jQuery) |
| Source maps, README, licences, .psd sources | 100% | Exclude from the ZIP — the Folder to ZIP tool skips maps and dot-files |
| Video or long audio | — | Cannot be compressed further; host it and stream from a URL |
Bundled versus loaded
Everything in the ZIP is inside the APK and available offline; that is the point of the ZIP route. But nothing stops a page from also loading a large asset from a URL when the phone is online — a product video, a map tile set, a 40 MB dataset. Split it that way: bundle what the app needs to be useful offline, load what is optional. The offline guide explains what a bundled page can and cannot do.