Because a tyre curves away from the middle of where the tyre rolls on the road, only the centre area is repairable. Sidewalls are not repairable.
The repairable area is defined as a percentage of the tyre’s “nominal” section width and thus varies by the size of the tyre. The repairable area is based on the centre line, eg. 82mm means 41mm on either side of the centre line of the tyre.
Using this handy REPAIRABLE AREA TREAD GAUGE, you can quickly find out if a puncture in your tyre is likely to be repairable.
Follow the printing instructions so that it is the right size, cut it out, read the tyre width off its sidewall, then put the centre line of the gauge in the middle of the tyre where the puncture is. If the puncture falls between the markings for that size tyre, it is probably repairable.