Estimation Calculator
Use the calculator for your own numbers and compare another example instantly.
The basic method
Round the factors to nearby numbers that are easier to multiply mentally. Keep the rounded values close enough to the originals that the estimate stays useful.
Worked example
For 26 × 604, one useful estimate is 25 × 600 = 15,000. That makes 15,000 a reasonable estimate for the exact product.
When to round one factor or both
If one factor is already easy to use, round only the more difficult factor. If both values are awkward, rounding both can make the mental math much faster.
Common mistakes
- Rounding so aggressively that the estimate loses meaning.
- Treating an estimate as the exact answer.
- Rounding in opposite directions without considering the effect.
Frequently asked questions
Should I always round to the nearest ten?
No. Choose tens, hundreds or other friendly values that make the arithmetic easy while staying close to the original numbers.
Is 15,000 a reasonable estimate for 26 × 604?
Yes. Rounding to 25 × 600 gives 15,000, which is close to the exact result.
Can an estimate be slightly high or low?
Yes. The goal is a useful approximation, not an exact match.