Why not use the KLM website to get the definitive information as this is subject to change.
Maximum Dimensions of Carry-on Luggage: 22in x 14in x 10in/55cm x 35cm x 25cm (length x width x height) Maximum Weight 22 lb/10 kg
2 pieces, each max. 23 kg (50 lbs) max.
Best check near the time of departure, if dealing via a Travel agent they should be able to help, but I doubt there would be any series deviation.