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Page Load Simulator

Estimate page load times on slow networks and phones.

Private by design

Your inputs stay on your device and are not sent to our servers. Optional usage analytics does not receive your files or tool inputs.

Preparing tool

How to use Page Load Simulator

Pick a kind of page or enter its sizes from your browser's Network tab.
Choose a network and phone, and play the load or scrub the waterfall.
Read first and largest paint, data cost and the changes that save the most time, and export the numbers.

Read the detailed guide →

What are the limits of Page Load Simulator?

A model of one HTTP/2 connection with TCP slow start and typical script costs; caching, priorities and server location change real results. Measure with Lighthouse or WebPageTest too.

Page Load Simulator

News site · 2.7 MB

Busy 4G5 Mbps, 120 ms latencyMid-range phone

6.6 s

Results

Kind of page

HTML KBCSS KBJavaScript KBFonts KBAll images KBLargest image KBScript filesImage filesServers (incl. third parties)Server time ms

Scripts

Rendering

Mobile data price₹10/GBGet real sizes from your browser’s developer tools (Network tab, transferred column) or a HAR file.

4G at a crowded station or in the evening rush.

Largest content appears at 3.7 s
Needs improvement: aim for 2.5 s on this network.
Something shows at 3.1 s
First Contentful Paint: until then the visitor sees a blank screen. Aim for 1.8 s.
Ready to use at 4.7 s
Scripts finish soon after the page appears.
Page weight 2.7 MB
About ₹0.03 of mobile data per visit at ₹10/GB. Aim for under 1.6 MB.
JavaScript 900 KB
About 0.9 s of processing on a mid-range phone. Aim for 300 KB or less (compressed).

Trim first

Defer scripts that are not needed for first paint−1.5 s
Halve JavaScript−1.2 s
Cut third-party scripts−0.5 s

Compress and resize images, and serve WebP or AVIF.
Load only the JavaScript a page needs; defer the rest.
Preload the largest image and self-host fonts with font-display: swap.
Test on a budget phone on 3G, not only on office Wi-Fi.

Each load is modelled on one HTTP/2 connection: DNS, TCP and TLS take three round trips, data flows through TCP slow start (initial window 10 packets) up to the network's speed, CSS and blocking scripts must arrive and run before first paint, and scripts cost processing time by device (about 0.3, 1 and 2.5 ms per KB on a laptop, mid-range and budget phone). Real pages also depend on caching, priorities and server location, so measure with Lighthouse or WebPageTest too.