Online Tool Store
Lowest Common Denominator Calculator
Find the lowest common denominator for a set of fractions, see the converted equivalents, and add or compare them without guesswork.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Math & Science
Lowest Common Denominator Calculator
Frontend preview — no upload or external service.
Result
Denominators 4, 6 and 10 have an LCD of 60: 3/4 = 45/60, 5/6 = 50/60, 7/10 = 42/60 — so 7/10 is the smallest of the three.
How the Lowest Common Denominator Calculator works
- Enter the fractions separated by commas.
- Read the LCD and the converted equivalents.
- Use the converted forms to add or compare, since fractions can only be added over a shared denominator.
The method
The lowest common denominator is the least common multiple of the denominators, found by taking each prime factor at its highest power across all of them.
4 = 2², 6 = 2·3, 10 = 2·5 → LCM = 2²·3·5 = 60
Multiplying all the denominators together also gives a common denominator — 240 here — but not the lowest, which means more simplifying later.
FAQ
Why not just multiply the denominators?
It works and gives a valid common denominator, but usually a much larger one. Using the LCD keeps the numbers small and often means the answer needs no simplifying at all.
What is the difference between LCD and LCM?
They are the same calculation. LCM is the general term for any set of numbers; LCD is what we call it when those numbers happen to be denominators.
Does this help with comparing fractions?
Yes, and it is the reliable method. Once every fraction is over the same denominator, the numerators can be compared directly.
How we compare
| Feature | Online Tool Store | A graphing calculator | A stats package |
|---|---|---|---|
| Shows converted fractions | ✓ | ✗ | ✓ |
| Prime factorisation working | ✓ | ✗ | Sometimes |
| No sign-up | ✓ | ✓ | ✗ |
| Works offline once loaded | ✓ | ✓ | ✗ |
Lowest Common Denominator Calculator shows the prime factorisation, since that is the method that generalises beyond the two-fraction case.