Some objects which are one centimeter long include the radius of an American penny, the thickness of a standard notepad and the width of the average pinkie finger. A credit card is also used to estimate centimeters, as it measures 9cm x 5cm.
There are many objects which are one centimeter long. If you are looking for one centimeter exactly, you could also use the length of a staple, the box size of your average graph ruled paper and the width of most standard pens and pencils. Estimation of larger distances in centimeters is done using larger objects. These include the aforementioned credit card, a U.S bill note (15cm x 6cm), or a paperclip (3.5cm).
Estimating measurements, in the absence of actual measuring devices is incredibly useful. However, if you do have access to a measuring device, there are several ways to convert these units into centimeters. For devices such as rulers, centimeters are on the other side of inches, so this is simple. For those that only have inches, however, all you need to remember is that there are 2.5 centimeters per inch. If you need to break down larger numbers, that means there are 10 centimeters for every 4 inches, or 25 centimeters for every 10 inches.