To estimate means to make an educated guess about a number, amount, or value when you can't measure it exactly. When you estimate, you use what you know to get close to the right answer, even if you can't be perfectly precise.

In math class, you might estimate that 48 times 23 is about 1,000 by rounding to 50 times 20. At the grocery store, you might estimate whether you have enough money by adding up prices in your head: $3.99 plus $5.29 is roughly $9. Scientists estimate the number of stars in our galaxy. Contractors estimate how much it will cost to build a deck.

A good estimate requires thinking carefully about the information you have. If someone asks how many jelly beans are in a jar, you might estimate by figuring out how many fit in one layer, then multiplying by the number of layers you can see. That's much better than just randomly guessing “a million”!

The word also works as a noun: “My estimate is that we'll need two pizzas for eight people” or “The plumber gave us an estimate for fixing the sink.” An underestimate means guessing too low, while an overestimate means guessing too high.