The size of points is usually indicated on the left frame arm and consists of 3 digits. Suppose glasses have size 52-18-140. That is, the size of the lens is 52 mm, and the width bows over the bridge of - 8 mm. Length mumps, respectively - 14 cm.
For right choice of points you need to measure your face from two perspectives. The width is measured from temple to temple at eye level, where, in fact, in the future and will be glasses. Be aware that the bow also has a width that is why it is necessary to measure with a small margin.
For the convenience of measurement is also possible to use a ruler and pencil on a bridge on the ears. A kind of imitation points by which a ruler can measure the width of your face. Also, a ruler can measure the distance from the pencil on the nose to the end of the ear. As a result, you should get a number in the range from 100 to 200 mm. Thus, if you double-folded lens size and add to this the size of the bow over the bridge, and add 4 to 10 cm wide joints, you get a figure corresponding to the width of a human face, that these glasses are suitable.
In our example, the calculation is as follows: 52 + 52 + 18 = 122 mm. It is worth noting that different manufacturers of spectacle frames the same size may have different meanings. So remember that there is an error in the data values, so the figure can vary by plus or minus 6 cm. Similarly, the length of the ear hook can vary between 5 cm.
If you do not know what points can you come in the first place can pick them up in size over the bridge arch. To start from the value of your face Schirin subtract the size of the bow over the bridge, followed by 10 cm, which occur in the joints frames with bows. The resulting figure divide by 2 and you get the best size for you eyeglasses.