IEC 60793-1-20:2014 establishes uniform requirements for measuring the geometrical characteristics of uncoated optical fibres. The geometry of uncoated optical fibres directly affect splicing, connectorization and cabling and so are fundamental parameters requiring careful specification, quality control, and thus measurement. This second edition cancels and replaces the first edition, published in 2001, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:- the reference test method for all fibre types is changed to the video grey scale transmitted near field method from the refracted near field method;- the test lengths for all fibre types are now to be specified in the fibre's detail specification;- the core illumination wavelength for all multimode fibre types may now to be specified in the fibre's detail specification although defaults are given;- the core k-factor (decision level) is now to be specified in the detail specification for all multimode fibre types;- this edition is substantially more specific in describing the measurement;- data reduction and transformation is fully described;- the data reduction methodology for both refracted near-field and transmitted near-field methods are now unified and consistent. Keywords: measuring the geometrical characteristics of uncoated optical fibres