Everthing you need to know about Wheel sizes & Spokes (ETRTRO/Inches/French Std)

Here's a sweet little fact: 

The first (Geoff Apps-designed) 700C wheeled off-road bicycle was made in 1981.

It's all here, Inches vs ISO-5775/ETRTRO vs French.

Schwalbe :

http://www.schwalbetires.com/tech_info/size_markings

BikeCalc.com:

http://www.bikecalc.com/wheel_size_math
(Best read what is says about it first though)

There' s also this handy spoke calculator here:

http://spokes-calculator.dtswiss.com/Welcome.aspx?language=en

Both need updating for 27.5" wheels, but also note that 29ers or two-niners are mountain bikes and hybrid bikes that are built to use 700c or 622 mm ISO (inside rim diameter) wheels

From https://en.wikipedia.org/wiki/ISO_5775