Joined: Jan 2009
Posts: 44,172
Likes: 6,391
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
Seatpost diameters are in increments of 0.2 mm so being off by 1 mm is a lot. You need a caliper to measure it accurately. You can't match it up to a ruler.