This calculator only provides an approximation of speed. Please don't expect precision and accuracy.
This is spin-out top speed only and doesn't account for one's inability to push hard enough to spin out a hard gear, or for things like coasting down a steep grade. For instance, I can't spin out my Trek 1200 on flat land (51 MPH given a 150 cadence) and I've coasted my hybrid at a speed higher than I could achieve by pedaling in its highest gear. The circumference of various tire sizes listed are just gathered from Sheldon Brown's site and may vary significantly from your actual circumference.
2006 Trek 1200 Road bike Tires: 700x25 Chainrings: 30/42/52 Cassette: 12-13-14-15-17-19-21-23-25 2007 Specialized S-Works Langster fixed-gear track bike Tires: 700x23 Chainring: 48 Cassette: 16 2008 Mongoose Fraction BMX bike Tires: 20x1.75 Chainring: 30 Cassette: 11 2008 Surly Crosscheck Complete Cyclocross racing bike Tires: 700x32 Chainrings: 36/48 Cassette: 12-13-14-15-17-19-21-23-25 Sun EZ-TAD Recumbent "tadpole" tricycle Tires: 20x1.5 Chainrings: 30/42/52 Cassette: 11-32