Proportion Calculator
Solve the proportion A/B = C/X for the unknown X, computed as X = B*C/A. For A = 2, B = 5, C = 8, X is 20.
What this calculator does
The Proportion Calculator estimates your result instantly from the values you enter, using standard math & conversions formulas. Solve the proportion A/B = C/X for the unknown X, computed as X = B*C/A. For A = 2, B = 5, C = 8, X is 20. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About Proportion Calculator
The Proportion Calculator solves the proportion A/B = C/X for the unknown X. Given A, B, and C, it computes X = B times C divided by A.
Formula & Mathematical Calculation
X = f(A, B, C)
Calculated according to standard math formulas implemented in the calculator core.
Calculation Example
Enter A=2, B=5, and C=8, then Calculate. The X box shows 20, since solving 2/5 = 8/X gives X = 5 x 8 / 2 = 20.
Key Benefits
- Solves the proportion A/B = C/X for the missing value X
- Uses the cross-multiplication result X = B times C divided by A
- Blocks A = 0 with a clear error since it would divide by zero
How to Use this Calculator
-
Enter A and B
Type the first ratio's terms in the A and B fields. -
Enter C
Type the known term of the second ratio in the C field. -
Read X
Click Calculate and read the solved value in the X box.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- Proportion Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.