The OP means ISO559mm, but if one should ever walk into a bike shop in a foreign location, it might be handy to know:

There are eight different, non-interchangeable “26 inch” wheel sizes.

1) 26 x 1.25: bead seat diameter 599mm. Obsolete.
2) 26 x 1 1/4: bead seat diameter 597mm. Also known as Schwinn S6. Obsolete.
3) 26 x 1 3/8: bead seat diameter 590mm. Also known as 650A and EA3. This is also a common wheelchair tire size.
4) 26 x ?: bead seat diameter 587mm. Also known as 700D. Very obscure and obsolete size.
5) 26 x 1 1/2: bead seat diameter 584mm. Also known as 650B.
6) 26 x 1 3/4: bead seat diameter 571mm. Also known as 650C. Obsolete. Tires are still made, but uncommon.
7) 26 x 1: bead seat diameter 571mm. Known as 650C as well. Used today on time trial and triathlon bikes.
8) 26 x 1.0 to 2.35: bead seat diameter 559mm. The ubiquitous mountain bike tire size, descended from the American balloon tires of over a half century ago. Now made in a huge array of widths and tread patterns. In the wheelchair world, this smallest 26-inch size is sometimes referred to as “25-inch”.