There are a lot of different services claiming to analyse the speed of your website. Out of these we recommend two.
The first we recommend is provided by webpage test to measure the performance of your site. This tool provides very detailed performance information with the ability to choose the location of the request.
The second we recommend is running google Lighthouse from within the Chrome browser on your local computer. Running it locally is important, using the online pagespeed insights will result in the test being run from the US with simulated slowdowns which might not be reflective of your clients.
Have a read of our three part blog series on testing website performance, An introduction to website performance testing, Testing website performance with webpagetest.org, and Testing sitespeed with Google lighthouse
We also have a cool website speed comparison tool that measures your website speed and compares it against competitors found via semrush. It also pulls information from the Chrome UX Report so you can see how Google views your real world website performance.