Year 8 · Maths
Estimate Calculations by Rounding
How do you estimate an answer by rounding?
Round each number to one significant figure, carry out the simpler calculation, and write the result as an estimate using the symbol ≈. For example, 312 × 48 ≈ 300 × 50 = 15,000. Compare the estimate with the exact answer to check whether the exact answer is sensible.
Two worked estimates
- Multiplication: 312 × 48 ≈ 300 × 50 = 15,000.
- Division: 19.6 ÷ 3.9 ≈ 20 ÷ 4 = 5.
Examples: 4.87 + 19.2 ≈ 5 + 20 = 25 · 0.0473 to 1 significant figure is 0.05
Keep practising: Use the Year 8 Maths checklist
Try the estimate-then-check routine
Round both numbers to one significant figure, calculate the estimate, then compare its scale with the exact result.
Worked example: 49.7 x 19.8 is about 50 x 20 = 1,000. The exact answer is 984.06, so the estimate confirms the scale.
Understand the key idea
Estimating means rounding each number — usually to one significant figure — then doing the easier calculation in your head. The result is not the exact answer; it tells you roughly what the answer should be, so you can spot a calculation that has gone badly wrong. The symbol ≈ means "is approximately equal to".
Five further estimation questions with complete working
- 3.97 × 19.8 ≈ 4 × 20 = 80.
- 58.7 × 0.21 ≈ 60 × 0.2 = 12.
- 803 ÷ 19.8 ≈ 800 ÷ 20 = 40.
- 0.48 × 198 ≈ 0.5 × 200 = 100.
- 49.8 × 2.03 = 1010.94 is not sensible because the estimate is about 50 × 2 = 100. The correct exact product is 101.094.
Common mix-up
Rounding to one significant figure is not the same as rounding to one decimal place. To 1 s.f. 0.0473 is 0.05, while to 1 d.p. it is 0.0.
Try this first
- Estimate 312 × 48 by rounding each number to 1 significant figure.
- Decide whether 19.6 ÷ 3.9 ≈ 5 is a sensible check.
- Round 0.0473 to 1 significant figure and to 1 decimal place, and compare.
Ask: Your calculator says 2,000 — how could you tell quickly whether that is sensible?
Year 8 learners practise estimating answers by rounding.
The activities include Estimate By Rounding to One Significant Figure Using Decimal Numbers, Estimate Measures, Estimate with Decimals, and related practice. The checked support below includes worksheet, teaching, lesson, video. Open a resource in its provider's website and choose the format that best helps the learner explain the idea independently.
Activities covered
Finish one activity, then tap Done to earn one Den Drop ticket. You can earn up to 3 tickets each day.
Share this topic
Share this page with another parent, carer or learner. No personal details are added.
Choose a learning resource
Start with an explanation, then practise, then print. Labels show access and review status before you click.
What the icons and labels mean
Formats
Watch — a video explanation
Learn — a lesson or teaching page to read and work through
Practise — questions or activities to try
Print — a worksheet you can print
Cost and account
Free no payment or account needed for this resource
Free account needed no payment needed, but the provider asks you to create an account
Subscription part of a paid plan on that site
Check access access has not yet been confirmed, so it appears only under Everything
Review status
Verified match checked against this topic, with a visible check date
Reviewed, not fully verified reviewed, with some checks still outstanding
Awaiting review still waiting for review
Tell us how it went
This helped · Link or access problem · Not the right match
We show a free label only after checking the resource's own page. Access can vary by resource. Unconfirmed access appears only under Everything.
Watch it explained
watch a video explanation
Estimating calculations by rounding video
Best for: a clear explanation before you practise
Introduction to the Metric System
Best for: a clear explanation before you practise
Nothing in this step matches your filters.
Learn it properly
lessons and teaching pages
Estimation and rounding
Best for: worked examples and step-by-step teaching
Rounding and estimating
Best for: worked examples and step-by-step teaching
Estimating calculations worked examples
Best for: worked examples and step-by-step teaching
Choosing sensible estimates for measures worked-example lesson
Best for: worked examples and step-by-step teaching
Nothing in this step matches your filters.
Practise it
questions and activities to try
Nothing in this step matches your filters.
Print and finish
worksheets away from the screen
Estimating numerical calculations worksheet
Best for: pencil-and-paper practice away from the screen
Nothing in this step matches your filters.