Any company that produces something will be faced with the task of estimating effort. (A company that produces nothing only has to estimate how long they think they can keep afloat.) Whether you build hovercrafts or databases, someone is going to want to know how long you think it will take, so that they can then ask “can you do it in half that?”
Estimates are used by different people in different ways. Marketing use estimates to determine the maximum amount they can get away with charging for a product. Clients use estimates to work out the smallest amount they can get away with paying for a product. And the estimators themselves use the estimates to indicate their willingness to create the product in question - the higher the estimate, the more reluctant they are.
Estimates are usually based on some form of written requirement from the client. To get an idea of the size of the project, reformat this document using a standard font size, line spacing and margin settings. Then print it on 80GSM paper, and bind with a single 26/6 staple. Weigh this document, in grams (accurate to the 3rd decimal place) take away 6.738 and then multiply this number by 11.375. The resulting number is your estimate by weight, known as a heftimate. (Note that more important projects, such as tenders, may be printed on a better class of thicker paper, bound in folders with metal rings. These heavier documents will provide larger heftimates which in turn reflects the gravitas of the project.)
Heftimation in incredibly accurate, and takes the guesswork out of sizing a project. This means that projects are more likely to come in on budget, clients will be happier, and most importantly it means that no one will ever need to use the word “guesstimate” ever again.