Measuring hand luggage at the gate.
With on-line check-in, the only place that Ryanair can check hand luggage is at the gate.
Ryanair's hand luggage allowance is quite clear. 1 bag only, maximum measurements 55x40x20cm and weighing no more than 10Kg. Handbag, briefcases, laptop, duty free, camera etc. must fit inside this 1 bag. Any oversize or overweight bag will be charges £35/35 Euro.
I have little sympathy for those charged at the gate for oversize luggage. If this allowance is inadequate or you feel the charge is excessive, you always have an option.