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P4 standards are a set of measurements allowing the accurate construction of a model railway to a scale of 4 mm to 1 foot (or 1:76.2).

For standard gauge track these standards translate to a scale model track gauge of 18.83 mm. The 5'3" Irish broad gauge has also modelled in 4 mm scale with 21 mm gauge track to P4 standards. Several successful models of narrow gauge prototypes with a corresponding narrowing of the model's track gague have also been produced to P4 standards.

P4 is accurate to scale for 4 mm to 1 foot scale modelling, while other track gauges such as specified for 00 (16.5 mm) and EM (18.2 mm) when used for standard gauge prototypes portray a less accurate approximations.

As well as a track gauge, P4 also specifies the exact wheel profile and track parameters to use, which are largely an exactly to scale version of real life standards.

P4 standards are promoted worldwide by the Scalefour Society, which is based in the United Kingdom. Details of the society can be located at the Scalefour Society website details of which are below. The EMGS also provides support for modelling to P4 standards, many P4 modellers belonging to both societies.

Owing to space constraints and the necessity for the construction in model form of tighter than prototypical track curves, there are still a couple of compromises within P4 standards. For some railway modellers who feel that this is unnecessary an exact set of standards has been formulated and are known as Scalefour standards also known as S4. These standards are not to be confused with the Scalefour Society.

• CLAG Some of the most innovative modelling in p4 you will ever see
• Scalefour Society, supporting modelling to P4 standards
• EM Gauge Society, supporting modelling to both EM and P4 standards

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