If it is a simple nucleic acid marker, just look at the relationship between the marker band size and your target band, and try to choose a marker with a target band close to the molecular weight, or a marker with more bands near the target molecular weight.

In addition, if the target molecular weight is small and the gel concentration is usually high, the marker with too large molecular weight can't be used, for example, only a band of 200bp is detected, so it is more suitable to use the marker with the maximum molecular weight of 1000 or 500.

If the molecular weight is large, such as a few k, you may choose a marker with a maximum of 23K, such as lamda HindIII. Otherwise, the gel concentration is not appropriate, and the marker band can not be separated, which will affect your judgment on the molecular weight of the target molecule.

In the past, 2000 and 15000 were the most commonly used markers in the laboratory, which could cover most of the molecular weight detection.