Free Unit Converter

Conversions of area, density, energy, force, length, mass, power, pressure, speed, temperature, volume and bytes.
http://www.flowmeterdirectory.com/flowmeter_unit_converter/index.htm

Pumpuniversity: calculators, conversion programs and theory

On line calculators, conversion programs and theoretical information on pumps.
http://www.pumpuniversity.com

Martindale's 'The Reference Desk: Calculators On-Line'

A very extensive set of Java script based online calculators covering many subjects.
http://www.martindalecenter.com/Calculators.html