The right handlebar width for an omafiets (the traditional Dutch city bike) matters for comfort and control. As a rule, the handlebars should be about as wide as your shoulders: sitting on the bike with your hands on the grips, your elbows and shoulders should be at a natural, comfortable angle.
Frame sizes 49 and 50 usually come with handlebars of around 530–560 mm; for frame sizes 57 and 61, 580 mm and wider is common.