This page makes free printable 5th grade GCF and LCM worksheets on demand: press the button and you get a new sheet of 20 problems with a matching answer key, ready for US Letter or A4 paper. Right now the generator is set to problems such as LCM of 36 and 30 (answer 180) and LCM of 12 and 9 (answer 36); press the button again and the numbers change while the skill stays the same.
‘New set of problems’ opens the generator in its own tab. There you can change the problem count and turn the answer key on or off. ‘Print or save as PDF’ opens the print dialog — choose Save as PDF in the printer list to keep the file. The sheet fits US Letter and A4, and the answer key prints on its own page.
Prime factorisation is the general tool: break both numbers down, take the shared primes for the factor and all of them for the multiple.
Factors and multiples pull in opposite directions: factors divide into a number, multiples are built from it. A question like LCM of 36 and 30 answers 180, and knowing which direction the question is asking is half the battle.
The greatest common factor is what simplifies a fraction; the lowest common multiple is what gives it a common denominator. Both jobs turn up constantly, which is why this topic is worth being fast at.
This sheet uses pairs built from factors 2 to 6, small enough to be listed out and large enough to make listing a slow method, and a typical line looks like GCF of 20 and 24.
These 5th grade GCF and LCM worksheets are commonly aligned with the number system strand for grades 5 and 6, and the skill appears in most curricula somewhere around this point.
| # | Problem | Answer | What to check |
|---|---|---|---|
| 1 | LCM of 36 and 30 = | 180 | Watch for: stopping at a common factor rather than the greatest |
| 2 | LCM of 12 and 9 = | 36 | Check: leaving the factorisation incomplete |
| 3 | GCF of 21 and 18 = | 3 | Look at: missing one in a factor list |
| 4 | GCF of 6 and 14 = | 2 | Ask about: multiplying the two numbers for the lcm |
| 5 | GCF of 20 and 24 = | 4 | Watch for: treating a prime as having no factors |
| 6 | LCM of 18 and 42 = | 126 | Check: swapping factor and multiple |
Try GCF of 21 and 18 together before letting the child start alone. The answer to GCF of 21 and 18 is 3, and talking through how it was reached takes about a minute and saves several minutes of guessing later in the sheet.
The item LCM of 12 and 9 is worth doing slowly. The answer to LCM of 12 and 9 is 36, and the route to it is the route every other problem on this sheet takes — which is why the sheet has 20 of them rather than one.
Because the numbers are random, there is no shared answer list to look up: the key printed behind your sheet is the only one that fits it, and it shows 180 for LCM of 36 and 30.
Keys are produced by the same code that produces the questions, so a mismatch between question and answer is not possible on these sheets.
The sheet is laid out to fit one page on both US Letter and A4. Leave the browser scaling at 100% and turn headers and footers off, and the 20 problems land inside the margins on either paper size.
Portrait orientation is what the sheet is designed for. Landscape works but wastes about a third of the paper, so leave the orientation alone unless you have a reason.
One sheet of 5th grade GCF and LCM worksheets a day for two weeks will tell you more about where a 5th grader actually stands than any single long assessment.
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Free printable math worksheets from a working math academy director in Korea. Problems come from our own code, not from a published workbook. Every sheet prints on US Letter or A4 with its answer key. All worksheets · Worksheet generator · Korean site
Last updated: 2026-09-13