Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Missing term value
12.0000
Solved for
D
Simplified A
3.00
Simplified B
4.00
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter a.
- 2Enter b.
- 3Enter c.
- 4Enter d (0 to solve).
- 5Read your missing term value on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Solve A:B = C:D for any missing term. Leave one field at 0 to solve for it.
Worked example
Using the values the calculator loads with:
Inputs
- A: 3
- B: 4
- C: 9
- D (0 to solve): 0
Results
- Missing term value: 12
- Solved for: D
- Simplified A: 3
- Simplified B: 4
What each field means
Inputs
- A
- The a used in the calculation. Starts at 3 so you have a working example on load.
- B
- The b used in the calculation. Starts at 4 so you have a working example on load.
- C
- The c used in the calculation. Starts at 9 so you have a working example on load.
- D (0 to solve)
- The d (0 to solve) used in the calculation. Starts at 0 so you have a working example on load.
Results
- Missing term value
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Solved for
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Simplified A
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Simplified B
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the ratio calculator work?
Solve A:B = C:D for any missing term. Leave one field at 0 to solve for it.
What do I need to enter?
4 values: a, b, c, and d (0 to solve). Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the missing term value result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Ratio Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/ratio
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/ratio" target="_blank" rel="noopener">Ratio Calculator — RevenueLab</a> (2026).</p>
Source: [Ratio Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/ratio) (2026).