Website load time by connection

Website load time by connection: what it is for

A heavy page is slow to open on phones, and every extra second makes people give up. This calculator estimates your page's network time on four connections, from slow 3G (0.4 Mbps and 400 ms, WebPageTest's 3G Slow profile) to Wi-Fi, including Lighthouse's default mobile profile (1.6 Mbps and 150 ms).

You enter the weight of the HTML, CSS, JavaScript, images and fonts, the number of files and domains, and see the total weight, how much each part accounts for and the estimated time, adding the connection round trips and the transfer. You can simulate switching the images to WebP and see the gain.

How to use

1. Open the browser's Network tab and note the weight of each file type.
2. Fill in the weights, the number of files and the number of domains.
3. Compare the times by connection and see what weighs the most.

When to use it

• Showing a client why the site is slow.
• Deciding what to optimize first.
• Comparing before and after compressing images.

Frequently asked questions

Where can I see my page's weight?

In Chrome, open the developer tools (F12), go to the Network tab, reload the page and look at the bottom bar: it shows the number of requests and the data transferred. The type filter separates JS, CSS, images and fonts.

Which speeds does the calculation use?

Slow 3G: 0.4 Mbps and a 400 ms round trip (WebPageTest's 3G Slow profile). Typical phone: 1.6 Mbps and 150 ms, the mobile profile Lighthouse uses by default. Good 4G: 9 Mbps and 60 ms. Wi-Fi or fiber: 50 Mbps and 20 ms. Real connections vary a lot; use it for comparison.

Is it the same as the PageSpeed score?

No. PageSpeed measures metrics such as LCP and INP by actually running the page, including the time to execute JavaScript and paint the screen. This calculation only estimates network time, which is usually the largest part on phones, and helps you see the effect of making the page lighter.

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