**In mathematics, benchmark numbers are predefined numbers that assist in estimation of an unknown quantity.** Benchmark numbers tend to be multiples of 5 or 10.

Benchmark numbers can be used in a variety of estimation problems. They are often found on number lines and labeling known quantities, for example, a jar of pennies labeled with "100 pennies" next to a much larger unlabeled jar of pennies. In that example, knowing the volume that 100 pennies take up can help in estimating how many pennies are in the larger jar.

The concept of benchmark numbers comes from the generalized definition of a benchmark, which is a standard known quantity by which other quantities can be measured.