One page. A one-page resume carries a contact block, an optional two or three line summary, three to five roles, education, and a compact skills line or block. Recent roles get three to five bullets; roles older than about eight years get one line each or a single "Earlier roles" line with titles, employers and years. Every bullet is an action verb plus a task plus scope in the units the job actually uses — tickets closed, beds covered, accounts managed, containers deployed, pupils taught. Use it if you have under roughly ten years of relevant experience, if you are changing fields and only part of your history is relevant, or if you are applying somewhere that will be skimming quickly: campus recruiting, high-volume retail and hospitality, agency submissions. One page does not mean one page of tiny text. If you are at 9pt Calibri with 0.3 inch margins to make it fit, you have a two-page resume with a formatting problem.
Two pages. Two pages is the default once you have more than about a decade of relevant work, or once the role requires evidence a single page cannot hold: a systems and tools list, named certifications, clinical procedures, regulatory frameworks, languages. Structure matters more than length here. Put your name, contact details, summary, skills and your current or most recent role on page 1, and let page 2 carry older roles, education, certifications and anything optional. Assume page 2 is skimmed, not read. Keep older roles to two or three bullets each and drop anything from before roughly the last 15 years unless it is genuinely load-bearing — a licence, a qualifying period, a named employer that still carries weight in your field. In the UK, Ireland, Australia, New Zealand and much of the EU, a two-page CV is normal at any level, and a one-page CV can read as thin for an experienced candidate. In the US and Canada, one page remains the safer default early on. Check what is customary where you are applying.
Three or more pages. This is a different document, not a longer resume. Academic CVs list publications, conference papers, grants, teaching, supervision and service in full, in the citation style of the field, and they run as long as the record. US federal resumes submitted through USAJOBS ask for detail no private employer wants — hours per week, supervisor contact details, salary history, series and grade — and commonly run four to six pages. Clinical and medical CVs list licences by state or country, registration numbers, procedures, rotations and continuing education. Use this length only when the receiving system or the posting asks for it. If you work in one of these fields but are applying to a company, keep a two-page resume alongside your CV and send that instead.
The one-and-a-bit trap. Most bloated resumes are not three pages, they are 1.3. The fix is nearly always editing rather than formatting. Cut the summary from five lines to three. Delete bullets that describe the job description rather than your performance. Merge two thin roles at the same employer into one entry with a date range and a title progression. And compress weak bullets that spend two lines saying very little:
Weak — two lines, no scope
Responsible for managing the company's social media accounts and creating content on a regular basis.
Strong — one line, more information
Ran 4 brand accounts, publishing 20 posts a week and growing combined followers from 12k to 31k in 11 months.
Do that four or five times and the page count takes care of itself. If after real editing you are still at 1.5 pages, expand instead: add scope numbers to your top three bullets, add a certifications block, and build page 2 to at least three quarters full.