Key takeaways
- Build a list of relevant businesses first, then measure each website — there is no reliable public list of “slow sites”.
- Use Google PageSpeed Insights and focus on Core Web Vitals: LCP, INP and CLS.
- Lab scores vary between runs; test more than once and prefer real-user field data where it is available.
- Explain speed in business terms and pair the problem with a clear, realistic fix.
What counts as a slow website
Google’s Core Web Vitals are the most widely used yardstick. A page is considered “good” when, for most visits:
- 01Largest Contentful Paint (LCP) — the main content appears within 2.5 seconds.
- 02Interaction to Next Paint (INP) — the page responds to taps and clicks within 200 milliseconds.
- 03Cumulative Layout Shift (CLS) — the layout shifts by less than 0.1 while loading.
Free tools for measuring speed
Google PageSpeed Insights is the simplest starting point. It shows field data from real Chrome users (the Chrome UX Report) when a site has enough traffic, plus a lab test powered by Lighthouse with specific suggestions. Many small business sites do not have enough traffic for field data, so you will often rely on the lab result. Lighthouse in Chrome DevTools and WebPageTest are useful for a second opinion.
A step-by-step process
- 01Build a list of businesses in your target sector and area — in ClientFinch, by SIC code, location and status.
- 02Find each company’s website and test the homepage in PageSpeed Insights on the mobile setting.
- 03Run the test two or three times; record the typical LCP, INP (or Total Blocking Time in lab tests) and CLS.
- 04Note the main causes the report lists, such as large images, render-blocking scripts or slow server response.
- 05Save the companies with clear problems and write the key figures and causes in your notes.
Interpreting results fairly
Lab tests simulate a mid-range phone on a slower connection, so results can look worse than many visitors experience, and scores move between runs. Avoid quoting a single score as if it were definitive. Focus on what a visitor sees — “the main image takes several seconds to appear on a phone” — and on causes you can fix.
Presenting speed as an opportunity
Business owners care about enquiries, not milliseconds. Explain that slow pages make visitors more likely to leave, link speed to the actions that matter on their site, and outline the likely fix — compressing images, removing unused plugins or improving hosting. A short before-and-after estimate is more persuasive than a long technical report.
This guide is general information, not legal advice. For data protection questions, see the ICO’s direct marketing guidance.