hueyhoolihan

first things first. find the size of the rim.

if the old tire was indeed on the rim and you could get it off without destroying it, then most likely the rim is a 700c (622mm in diameter). if the bead had been destroyed and was on the rim, or had to be destroyed, or was destroyed while getting it off the rim, the rim may very well be a 27" (630mm in diameter) rim. i would beg borrow a wheel that is known to be one or the other and compare it, side by side. the 27" wheel, without tire, will sit about 7mm higher off the ground than a 700c wheel.

a pic of the bike (or age, or make, or model) would be of immense help here.

and BTW, if it turns out that it is, indeed, a 27" tire, these days, a 27x1 1/4 is readily available online, but there is only one tire, that i know of, that is available in a 27x1 size and that is made by Panaracer.

one would think that if the tire was on the rim, as mentioned, the rim is a 700c rim, but i've seen people that destroyed a tire bead while attempting to get a 700c tire on a 27" rim. they even thought that they had succeeded, but, in reality, they had simply destroyed the tire in the process.