Convert Anything: http://www.onlineconversion.com
Everything You Wanted to Know About Hardness (and then some): http://www.calce.umd.edu/TSFA/Hardness_ad_.htm
A Handy Online Scientific Calculator: http://web2.0calc.com/
Online Calculation of an Object's Volume: http://www.onlineconversion.com/object_volume.htm
Online Calculation of an Object's Surface Area: http://www.onlineconversion.com/object_surfacearea.htm
Mathematical Formulas Galore: http://www.sosmath.com/tables/tables.html
The Engineers Tool Box: http://www.engineeringtoolbox.com/
The NIST Ceramics Division: http://www.nist.gov/mml/ceramics/