A few details from the sidewall help start a tyre enquiry.
Start with the sidewall
A marking such as 205/55 R16 describes the tyre size. Copy the whole marking, including any following load and speed characters. Your vehicle handbook gives the tyre specifications for your car.
Check from a safe place
Read the tyre only when the car is stationary and you can approach it safely. If access is awkward, share the registration or vehicle details instead.
Let the fitter confirm
Tyres can differ between the front and rear wheels. A fitter should confirm the vehicle requirements before recommending or supplying a replacement.
General information for this fictional demo. Ask a qualified tyre professional about your vehicle.