Landmark Numbers

Contents

1. How Landmark Numbers Work
2. Examples of Landmark Numbers
3. Using Landmark Numbers in Calculations
4. Difference Between Landmark and Convenient Numbers
   1. Landmark Numbers
   2. Convenient Numbers
   3. Key Differences at a Glance
5. References
6. ‌Videos

Landmark numbers are commonly used reference points that make mental math easier and improve numerical understanding. These numbers, often multiples of 10 or other familiar values, serve as benchmarks for estimation and calculation. They can be particularly helpful when approximating large values or performing addition, subtraction, multiplication, and division.

How Landmark Numbers Work

• Reference Points: Landmark numbers, like 10, 100, 1000, or common fractions (1/2, 1/4, etc.), act as anchors for understanding other numbers.
• Mental Math: They help simplify calculations by allowing you to break down problems into easier steps, often involving addition or subtraction to reach a landmark number according to a YouTube video on addition strategies.
• Estimation: When dealing with large or unfamiliar numbers, landmark numbers can be used to estimate the approximate value says a Reddit thread on landmark numbers.
• Number Sense: By understanding landmark numbers, you develop a better sense of the relationships between numbers and their relative magnitudes.

Examples of Landmark Numbers

• Multiples of 10: 10, 20, 30, 40, 100, 1000 are common examples.
• Fractions and Percentages: 1/2 (50%), 1/4 (25%), 1/3 (33.33%) are often used as landmarks.
• Other Familiar Values: 1000 (one thousand), 1,000,000 (one million), or even specific dates like 1776 (year of the US Declaration of Independence) can be landmarks, according to Mathnasium.

Using Landmark Numbers in Calculations

• Addition: When adding 23 + 48, you might think of 48 as close to 50, and add 23 + 50, then subtract 2.
• Subtraction: When subtracting 79 from 100, you can use 100 as a landmark and subtract 79 from it (100 – 79 = 21).
• Estimation: To estimate 32 * 18, you might round 32 to 30 and 18 to 20, then calculate 30 * 20 = 600.

Difference Between Landmark and Convenient Numbers

Both landmark numbers and convenient numbers are tools used to simplify calculations and make numbers more approachable, especially in mental math, but they differ slightly in their core function.

Landmark Numbers

• Purpose: Primarily used as reference points or anchor numbers to understand and relate other numbers to.
• Function: Provide a “sense of scale” or context for unfamiliar quantities.
• Examples: 10, 100, 1000, multiples of 10 or 25.
• Analogy: Like a lighthouse guiding you through the vast expanse of the ocean of numbers.
• Application: Used for approximating large values, understanding the magnitude of quantities, and making estimations.

Convenient Numbers

• Purpose: Numbers that are easy to work with mentally, making calculations simpler and faster.
• Function: Facilitate mental arithmetic by simplifying operations like addition, subtraction, multiplication, and division.
• Examples: Numbers ending in zero, multiples of 5, or numbers that easily add up to multiples of 10.
• Relationship to Landmark Numbers: Many landmark numbers are also convenient numbers because they are easy to calculate with.
• Application: Employed for mental math strategies where exact answers are needed or close approximations suffice.

Key Differences at a Glance

 

Landmark numbers provide the framework for understanding, while convenient numbers provide the tools for calculation within that framework.

References

“Use Landmark Numbers.” 2025. @Tregoningmich. 2025. https://mentalcomputationstrats.weebly.com/use-landmark-numbers.html.

‌“What Is Benchmark ⭐ Definition Facts & Example.” 2024. Brighterly Knowledge Base. January 11, 2024. https://brighterly.com/math/benchmark/.

‌“What Are Compatible Numbers ⭐ Definition, Examples & Facts.” 2024. Brighterly Knowledge Base. January 6, 2024. https://brighterly.com/math/compatible-numbers/.

Habecker, Duane. 2020. “Number Talk Strategies – All of Them.” Google Docs. 2020. https://docs.google.com/document/d/1415yQt41D09mczSF3SlTf3tCTHefAKffPtaO8bA7x_Y/edit?tab=t.0.

‌Landmark. 2020. “Landmark Fractions and Decimals.” Google Docs. 2020. https://docs.google.com/document/d/1r-GSpFUhu3ZuBOQisOn1Zi0dNKEt15Sqz4ZqVcdebwA/edit?tab=t.0.

‌“Using Landmark Numbers to Add on the Open Number Line.” dreambox. Accessed August 14, 2025. https://info.discoveryeducation.com/rs/063-SDC-839/images/3_using_Landmark_Number_to_add.pdf.

“Number Magnitude: What Is It and Why Should I Teach It?” 2024. Teaching with Jillian Starr. December 8, 2024. https://jillianstarrteaching.com/number-magnitude-number-size/.

‌“Landmark Numbers.” 2023. mkodama.org. 2023. https://mkodama.org/content/landmark-numbers/.

‌“What Children Know and Need to Learn about Operations | DREME TE.” 2025. stanford.edu. 2025. https://prek-math-te.stanford.edu/operations/what-children-know-and-need-learn-about-operations.

Sieglera,Robert S. and Clarissa A. Thompson. “‌Numerical Landmarks Are Useful — Except When They’re Not.” 2013. siegler.tc.columbia.edu. November 24. https://siegler.tc.columbia.edu/wp-content/uploads/2019/02/2014-Siegler-Thompson-fac.pdf.

“Dimensions Math Letters Home Dimensions Math Home Connection.” Singapore Math Inc. Accessed August 14, 2025. https://singapore-math.s3.us-west-2.amazonaws.com/BLMs/DM_2_LETTERHOME_8.pdf.

‌“2.1.1A Numbers, Representation, and Place Value | Minnesota STEM Teacher Center.” 2023. scimathmn.org. 2023. https://stemtc.scimathmn.org/frameworks/211a-numbers-representation-and-place-value.

‌Numbers. 2023. “Compatible Numbers | Definition & Examples – Lesson | Study.com.” study.com. 2023. https://study.com/academy/lesson/what-are-compatible-numbers-definition-examples.html.

‌Shelley. 2020. “The Building Blocks of Number Sense.” The Write Stuff Teaching. November 13, 2020. https://thewritestuffteaching.com/the-building-blocks-of-number-sense/.

‌“98thPercentile.” 2019. 98thpercentile.com. 2019. https://www.98thpercentile.com/blog/place-value-of-numbers/.

‌“Number Sense | EBSCO.” 2024. EBSCO Information Services, Inc. | http://www.ebsco.com. 2024. https://www.ebsco.com/research-starters/mathematics/number-sense.

‌“Addition Strategies Progression | Department of Education.” 2025. maine.gov. 2025. https://www.maine.gov/doe/pl/math/addition.

‌North. 2025. “Numbers That Built a Nation.” Mathnasium. July 2025. https://www.mathnasium.com/math-centers/northbethesda/news/numbers-built-nation-g.

‌“Landmark numbers.” 2021. reddit.com. 2021. https://www.reddit.com/r/math/comments/ntrt33/landmark_numbers/.

‌Bader, B.W. 2009. “Constrained and Unconstrained Optimization.” Comprehensive Chemometrics, 521–51. https://doi.org/10.1016/b978-0-444-64165-6.01020-x.

‌“Benchmark Numbers: Definition with Examples.” 2022. SplashLearn – Math Vocabulary. April 27. https://www.splashlearn.com/math-vocabulary/number-sense/benchmark.

‌“Compatible Numbers.” 2022. SplashLearn – Math Vocabulary. April 27. https://www.splashlearn.com/math-vocabulary/number-sense/compatible-numbers.

“Using Benchmark Fractions to Compare Fractions – Alyssa Teaches.” 2021. Alyssa Teaches. January 15, 2021. https://alyssateaches.com/benchmark-fractions/.

‌Benchmark fractions are common fractions that we compare other fractions to. They are simple fractions that students are familiar with. They’re helpful to use when comparing and ordering fractions that are harder to visualize, like 8/11, because they can help us estimate. For that reason, they’re also useful when teaching students how to estimate sums and differences of fractions. Generally speaking, benchmark fractions are 0, 1/2, and 1. These are the numbers I’ve used with 4th grade students. With 5th graders, I might use 0, 1/4, 1/2, 3/4, and 1.

‌Videos