I have 27 x 1 1/4 inch tires on my bike and need to buy new tubes. Can I use 700c or just 27 inch?
The size of the tube is usually written on the box. Tubes stretch a bit so they fit a variety of sizes. For a 27 x 1 1/4 tire you would need one that says 700x32 which is the equivalent new size of tube, although both the old system and new system are usually written on the packaging. This size is very common and you should be able to purchase the tube at any cycling store, or sports store that sells bikes. If you don't have any in your area, you should also be able to purchase tubes at any department store that sells bikes.
Also make sure that you get the right valve type. Schrader is the same valve that is used on cars, while Presta is the only found on bikes. An older 27 inch wheel will almost certainly use a Schrader valve. You should be able to see the difference quite easily. Also, there are different lengths of valves, although those are usually only found on Presta Valves. This can be a concern if you have deep rims. I try not to use valves that are too long for my rims because its sometimes difficult to attach the pump in these circumstances. Although having too short of a valves can make it impossible to attach a pump.
Here is a picture of a box showing the sizes of tires that the tube is designed for. This tube will fit tires from size 700x25 to 700x32, or in the case where you have older wheels like yourself, will fit 27 x 1.00 to 27 x 1 1/4. It has a presta Valve.
Yep, a standard 700C tube will fit a 27" tire (and most tube boxes bear multiple markings to indicate this). Just convert the inch width to mm to get the width of the 700C tube, if the box doesn't say the inch size.
Tires, of course, are a different matter -- there is enough difference in rim diameters between 27" and 700C tires (which don't stretch like tubes) that one will not fit the other.