How strict are Ryanair staff on the size of cabin baggage.I dont mean I am going to go well over their size limits.
I have measured some trolley cases but with the wheels the size is going about 2cm over.
No problem; it needs to fit into their overhead lockers if it doesn't that's a problem and 2 cm over can fit in. Like grasscarp says, they look and so long as they know it could fit they let you take it on. However, make sure it doesn't weigh more than 10kg as a lot of ryanair drop offs can catch you on this.