Euro cylinder measuring guide
How to Measure a Euro Cylinder
Euro cylinders are measured from the centre of the fixing screw hole to each end of the cylinder. Record both sides separately, then choose the cylinder type and size that matches your door.
Measure the A and B sides
Remove the cylinder if you can
Open the door, undo the retaining screw on the edge of the door, turn the key slightly to line up the cam, then slide the cylinder out. Measuring the loose cylinder is usually more accurate than measuring it in the door.
Measure from the fixing screw to one end
Place the ruler on the centre of the fixing screw hole and measure to the end of the cylinder. This is one side of the size, often written as side A.
Measure from the fixing screw to the other end
Keep the ruler on the centre of the screw hole and measure to the opposite end. This gives side B. The overall size should equal side A plus side B.
Match the inside and outside correctly
For offset cylinders, the two sides are different. Match the inside and outside before ordering, especially for thumbturn cylinders where the turn side must face indoors.
Common measuring mistakes
Measuring the overall length only
A 70mm cylinder could be 35/35, 30/40, or another split. Always record both sides.
Measuring from the cam
Use the centre of the fixing screw hole as the reference point. The cam position can mislead the measurement.
Reversing an offset thumbturn
If one side has a thumbturn, confirm which side faces inside before choosing the size.
Choose the right euro cylinder type
Once you have the measurements, pick the matching cylinder style.