Your tire is the "traditional" size road tire that was "standard" prior to around 1980 or 1985. At that time, the 630 size was commonly sold with markings of 27 x 1 1/8 or 27 x 1/4. (That means it fits on a rim that is 27 inches high, and the tire has an inflated width of 1 and 1/8th inch.
Inches are good enough for REAL Americans...that metric stuff sounds kinda....kinda, well kinda French. Let that metric stuff in the schools...pretty soon our school kids will be drinking wine instead of beer, riding bikes instead of playing baseball...metrics are dangerous stuff.
Most Wal-Marts and K-Marts carry a ten buck version that is sturdy, but heavy. To get a light Bontrager or Continental tire in that size, you would need to visit a good bike shop.
A bike store can verify that the current tire is the correct tire for your rim. Sometimes a used bike will be sold with a tire that is too narrow or too wide for the design of the rim.