Yes, it does appear to be 11 which is confirmed by your photo with the perfortion gauge. There are four different Scott numbers: 498, 525, 544 and 545 for this 1c Washington stamp design. The first number is printed on a flat plate press, the second is printed on an offset press and the last two are printed on a rotary press. The two stamps printed on a rotary press differ in the dimensions of the printed design. All four have perforation 11 on all four sides.
A resource that is helpful in identifying US stamps is theswedishtiger.com
Can you tell me which # is this stamp 4 sides is 11 perforation. Please advise I know one member said the stamp is a offset I'm attaching one more picture it doesn't look offset to me but well you guys are the experts. Thank you Mara