How it works
These estimating sums worksheets for 3rd grade open on eight 3-digit sums: round both numbers to the nearest 100, add the round numbers, then find the exact sum. Other sheets round to tens or thousands or estimate differences.
Read the full guide
Round, add, then check
412 + 289 is about 400 + 300 = 700, and the exact sum is 701. Every problem has an estimate line, ___ + ___ = ___, and room for the exact answer, so the estimate is used: an exact answer of 601 or 7,001 would stand out against 700.
Tens or hundreds
Common Core grade 3 rounds to the nearest 10 or 100 (3.NBT.1) and uses estimates to judge answers (3.OA.8). 3-digit sums, rounded to tens: 438 + 247 gives 440 + 250 = 690 where hundreds give 600; the exact sum is 685. The thousands sheet and the exact sums on Sums past 1,000 go past grade 3.
- An estimate can land on the exact sum, as in 79 + 61 = 140. The key shows both lines anyway.
- Sums past 100 and Sums past 1,000 are the sheets where a dropped digit shows against the estimate.
Questions and answers
How do you estimate a sum?
Round each number to the same place, then add the round numbers: 68 + 57 is about 70 + 60 = 130. The exact sum, 125, should be close to it.
Do you round to the nearest 10 or the nearest 100?
Either; the sheet name says which. Rounding 236 + 48 to tens gives 240 + 50 = 290, close to the exact 284. Rounding to hundreds is quicker and rougher.
Is estimating sums a 3rd grade skill?
Yes. Common Core grade 3 rounds whole numbers to the nearest 10 or 100 and asks pupils to judge answers with estimates that use rounding.
Are there estimating differences sheets too?
Yes, under Estimate a difference: 2-digit numbers with tens, 3-digit numbers with hundreds, and a sheet that mixes plus and minus.