Why it matters
Third-party tags are often the heaviest thing on a page. A video embed, a chat widget and a couple of pixels can add a megabyte and seconds of main-thread work, and none of it is code you control. The cost is easy to miss because each tag looks small in its own snippet.
This calculator uses a catalogue measured on the date shown: each tag's official snippet was loaded on a blank page in Chromium, counting every request it made. Main-thread time comes from third-party-web, which attributes script execution in HTTP Archive's Lighthouse runs to the company behind each domain. Pick your tags to see the totals against a budget, and which ones to load only when someone clicks.
How to use it
- Tick the tags your site loads.
- Set a budget and a connection speed.
- Read the totals and the cost per tag.
- Replace heavy embeds with facades, and remove tags you no longer use.
FAQ
Where do the numbers come from?
Transfer sizes and requests were measured on the date shown by loading each tag's official snippet in Chromium with an empty cache. Main-thread times are third-party-web's averages from HTTP Archive's Lighthouse mobile runs across millions of sites.
Why might my site's numbers differ?
Tags load different code for different accounts, and some only load their loader without a real account ID. Your container or configuration, caching and the visitor's device all change the cost, so use this for comparing and budgeting.
What is a facade?
A lightweight placeholder, such as a video thumbnail or a chat button, that loads the real third-party code only when someone interacts with it. It removes the cost for visitors who never click.
Why is main-thread time per company?
HTTP Archive attributes script execution to domains, and several tags from one company share domains. Counting each company once avoids double-counting tags like GA4 and Google Tag Manager.
