The legal minimum tread depth in the UK is 1.6mm across the central three quarters of the tyre. Below that it is a fine and three points per tyre.
The quickest home check is a 20p coin: push it into the tread and if you can see the outer band of the coin, the tyre is close to or below the limit and needs checking properly.
We measure tread free of charge and fit tyres the same day — details on our tyres page.
Most drivers change at 3mm rather than 1.6mm, because wet grip drops off sharply below that.