Almost every job page on this site shows a UK figure in pounds and a US figure in dollars, side by side, on the same page. The obvious next step would be to convert one into the other so you can see 'which pays more' at a glance. We don't do that, on purpose, and it's worth explaining why — because the reasoning applies to any salary comparison you do yourself, not just the ones on this site.
An exchange rate answers the wrong question
A currency conversion tells you what a sum of money would be worth if you physically moved it from one currency to another today. That's the right tool for booking a hotel room or wiring money abroad. It's the wrong tool for comparing what a salary actually buys someone living and spending in their own country, because the exchange rate says nothing about local prices, taxes, healthcare costs, or typical living expenses in either place.
A converted number can also swing significantly with exchange-rate movements that have nothing to do with either country's job market — the same two salaries can look meaningfully different this month than they did six months ago purely because of currency markets, even though nothing about the actual jobs changed.
What a fairer comparison actually requires
A genuinely useful UK-vs-US comparison needs to account for at least: relative cost of living in the specific area (not just the country as a whole — London and rural England can differ from each other by as much as some country-to-country gaps), the tax and take-home-pay system in each country (income tax bands, National Insurance vs. federal/state/FICA taxes, and how employer-provided benefits like healthcare are typically bundled into or separate from a US salary), and what's included in the headline figure (US job offers are often quoted alongside employer-paid health insurance, which the UK's NHS-funded system doesn't require an employer to separately provide).
None of that fits into a single multiplier, which is why converting the currency and stopping there would give a misleadingly precise-looking number built on an oversimplified comparison.
How to use the figures on this site instead
Treat the UK and US figures on each page as two separate, locally-meaningful numbers rather than one comparison. If you're actually deciding between a UK-based and a US-based offer for the same type of role, the pound and dollar figures here are a starting point for the market rate in each country — from there, look up cost-of-living comparisons for your specific cities, and check what benefits (health insurance, pension/401(k) matching, paid leave) are included in each offer before treating either headline number as the full picture.