None of the online converters are going to be accurate and will always give the closest Pantone shade only. The closest Pantone shade can have an accuracy between 60% to 85% to the original color. It is always suggested to use the original Pantone Shade Card to achieve the closest 95% + accurate Pantone color as even the surface on which you have printed the color which causee the color to look different in different environments. The Pantone Formula Guide has about all the colors and a large variance to the color specified by you. You must use the book to get the right answer.
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I would suggest moving from CS3 or CC to the latest Photoshop edition which would automatically update all the Pantone Libraries. Furthermore, the latest Photoshop edition will have few predefined colors, but not all the Pantone colors. To avoid the translation from CMYK to RGB you must use the Pantone Color Bridge Shade Card RGB to CMYK. This shade card also comes with the Pantone software that can be used to import the color bridge libraries in photoshop. Once you have this library installed from the color bridge, you will be able to access all the spot and process colors. The Coated & Uncoated color bridge set is a multi-purpose tool which could solve your need. It is best used for determining how Solid Colors will look when reproduced through the four-color printing process, as well as a HTML value reference for digital media display intent. This two-guide set features all the 1,845 PANTONE MATCHING SYSTEM Colors, some of which are missing as per your question shown side-by-side with their four-color process printed equivalents on both coated and uncoated paper, enabling printers and designers to quickly determine how closely Solid Colors can be matched in CMYK along with the software to install the libraries in photoshop.
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