There is no single number. It depends on whether you were UK resident in any of the three previous tax years, and on your connections with the UK.
This calculator works through the Statutory Residence Test and gives an indicative UK day count. The tax year runs from 6 April to 5 April. The result is an approximation, not tax or legal advice.
Christopher Eames. Qualified tax barrister specialising in UK tax residence and international tax planning. Based between London and the world's best surf breaks.
How the Statutory Residence Test works is set out in this guide.