The simple answer is that you need to get a tube which says it is 700 x [A range of widths], where the range has the number indicated on your bike tire.
Read on for more detail, including my recommended inner tubes and how to determine your tire width.
Recommended inner tubes for 700c wheels
There are a handful of different tire widths for 700c wheels and you need to make sure that you get an inner tube which is suitable. Too small and it may pop. Too big and it will be under-inflated and too soft. That being said, inner tubes are similar to party balloons in that the width can vary according to the amount that they’re inflated. That means you can use the same inner tube size for a range of different tire widths. Hence what I said a moment ago: pick a tube which is 700x[width range that includes your tire width].
Determining your tire width is normally a very simple process on modern bikes. Squat down next to your bike so that you can see the tire sidewall – this is the rubber strip that goes in a circle adjacent to the metal wheel rim. Look along this strip and you’ll likely see a number of different pieces of information printed or embossed into the rubber. This will probably include a series of numbers that starts with either “700 x …” or “700c x …”. The number that appears after this multiplication sign is your tire width in millimeters and should be between 22 and 50.
Take this tire measurement, compare it to the list below, and click the link for my recommended inner tube for your 700c tires.
Recommended inner tubes for 700c tires
700c x 22 tube
700c x 23 tube
700c x 25 tube
700c x 28 tube
700c x 30 tube
700c x 32 tube
700c x 33 tube
700c x 35 tube
700c x 38 tube
700c x 40 tube
700c x 42 tube
700c x 47 tube
Be aware that some inner tubes have a “Presta” valve. This looks different to the “Schrader” valve that is standard on most car tires and lots of bike tires. Presta valves are quite a bit slimmer and longer.
If your pump fits Schrader valves only then you’ll need to grab a little adaptor to go with it. This one is perfect.
Just screw it onto the valve and you’ll be able to pump the tube up just like a Schrader.
Need a quick lesson in changing an inner tube?
Keep some basic kit with you whenever you head out cycling:
A spare inner tube or two
Set of tire levers (I like plastic ones)
The entire job should then only take 1/2hr or so to carry out. There are 5 simple steps to fixing the flat tube:
Take the bike wheel off
Take off the old inner
Find out why it got a puncture (e.g. a piece of broken glass)
Fit the new inner tube
Reattach the bike wheel
For a video guide, have a watch of this.