What does a red circle with a number mean?
The maximum speed limit in miles per hour. You must not exceed the number shown.
A white circle with a red ring and a black number, for example 30.
What you must do
Keep at or below the posted speed. The limit applies until another speed-limit or national-speed-limit sign changes it.
Where you will see it
At the start of a speed-limit zone and repeated along the road.
Easy to confuse with: National speed limit
The plain diagonal-stripe circle means the national limit, not a posted number. See the national speed limit sign.
Test yourself
The theory test asks you to recognise signs like this one. Try the road and traffic signs quiz (with an easy and a hard set), or read the signs revision notes. Source: Know Your Traffic Signs.
Other common road signs
Meaning based on Know Your Traffic Signs and The Highway Code under the Open Government Licence v3.0. The sign image is our own simplified rendering for learning. Always check the current Highway Code on gov.uk. Not affiliated with or endorsed by the DVSA.