how do you find the uncertainty of a single measurement? For example, I am trying to find the uncertainty of 26 grams.

Please see answer below

Explanation:

The uncertainty will depend of the granularity of the instrument you use for the measurement.

For example, if you measure the length of a tabletop with a measuring tape with the smaller divisions given by the mm for example,then your measurement is limited by 1 mm (it cannot be better than that because your instrument doesn't have a finer division)

If you are using a digital scale to measure the weight of an object for example, and the scale displays in the readout 26.3 grams, then your uncertainty becomes 0.1 gram because that is the best your scale can read.

If on the other hand your scale reads no better than the gram, and gives you just 26 in the display, then the resolution of the scale is 1 gram, and that is what the uncertainty in your measurement is.

You have to report it as:  26 ± 1 g