Converting Earthquake values to Mw scale

Online conversion

Earthquake Seismometer Equations and Formulas Calculator

Documented formulae

Below are various documents containing formulae used. Unless otherwise stated all links are to PDF files

Basically all of these are interesting documents in their own right quite apart from the fact that they contain formulae for conversions.

Magnitude Scales And Quantification Of Earthquakes.
If you look at none of the others you should look at this one as it is the most relevant in terms of explanations, hence I have placed it at the top.

Empirical Global Relations Converting M S and m b to Moment Magnitude

Empirical Relationships For Magnitude And Source-To-Site Distance Conversions Using Recently Compiled Turkish Strong-Ground Motion Database

Local Relations For Converting Ml To Mw In Southern-Western Balkan Region

Performance of Different Regression Procedures on the Magnitude Conversion Problem

Documentation for the 2009 Canadian Composite Seismicity Catalogue (CCSC09)

Probabilistic Seismic Hazard Analysis in Thailand and Adjacent Areas by Using Regional Seismic Source Zones

Probabilistic Seismic Hazard Assessment for Vanuatu
The conversion data is on page 17, section 3.3.

Probabilistic Seismic Hazard Assessment For The Democratic Republic Of Congo And Surrounding Areas
The calculations are on the 4th page of the document, numbered page 332.

The Application Of Multiple Random Earthquake Simulations To Probabilistic Seismic Hazard Assessment In The Aegean Region

A forward test of the Decelerating–Accelerating Seismic Strain model to western south and central America

Preliminary Earthquake Hazard Map of Afghanistan

Broadband source modelling of the Nov 8 1997 Tibet 7.5 earthquake

Some definitions from Wikipedia

Richter Scale Magnitude
Surface Wave Magnitude
Moment Magnitude Scale

Other literature

Earthquake Magnitude Scales by James P. McCalpin (PDF)
Magnitude, Energy and Frequency of Occurrence A description of the Richter scale.
Relation between Seismic Moment M0 and Surface Wave Magnitude Ms A technical document from the University Of Tehran. (PDF 2007)