Size and Weight
Both pistols are categorized as subcompact and have identical dimensions. The pistols are 6.29 inches long, 4.17 inches high and both weight 19.75 ounces (unloaded).
Ammunition
The primary difference between these two handguns is the ammunition they carry. The Glock 26 is chambered for the 9 mm bullet and the Glock 27 uses the larger, and more powerful, .40 caliber bullet.
Capacity
The standard magazine on a Glock 26 has a capacity of 10 bullets; the standard Glock 27 magazine has a nine round capacity. Both pistols will accept magazines from larger Glock pistols of the same caliber; for example, a 17 round magazine from a 9 mm Glock 17 will operate in a Glock 26.