Math & Scientific
Proportion Calculator
Proportion Calculator is a browser-based calculator tool on CalcToolsBase. Free, browser-based Proportion Calculator with instant, clearly-labelled results. No signup, no uploads. To use it, enter your values and view the result directly in your browser — no signup and nothing to install.
Proportion Calculator turns your A, B and C into the unknown value using cross-multiplication of a∶b = c∶d. The maths runs locally, so nothing you enter leaves the page.
About this calculator
The Proportion Calculator gives you a quick way to solve a proportion for its missing term. Enter your A, B and C; it then returns the unknown value, worked out with cross-multiplication of a∶b = c∶d the moment you calculate. It runs fully in the browser, so it is private by design and works offline once loaded.
Designed for students and anyone scaling quantities, it returns the unknown value the moment you calculate — no sign-up, no uploads, and nothing stored between visits.
How to use
- Enter the three known values A, B, and C.
- Press Calculate to run the proportion calculator.
- Read the result: the missing value X that completes the proportion.
- Press Reset to clear the proportion calculator and start again.
Why use Proportion Calculator
Fast
Calculations run in your browser. No round trip to a server.
Private
Your inputs never leave your device. Nothing is uploaded.
Free
No signup, no paywall, no ads-in-results, no watermarks.
Accurate
Based on standard, well-established formulas.
Mobile-ready
Optimised for phones, tablets, and desktops alike.
Transparent
Honest disclaimers wherever browser limits or regional rules apply.
Common uses
Proportion when revising for exams
Proportion when preparing worksheets
Proportion for science-fair and project numbers
Proportion in research and report calculations
Proportion for verifying answers from a textbook
Proportion in competitive-exam practice
Technical notes
Proportion Calculator solves the proportion a/b = c/d for the unknown by cross-multiplication.
Inputs are taken exactly as entered, so check for typos before trusting an answer.
Because it runs locally, results appear instantly with no server round-trip.
FAQ
What does this calculator solve?
It solves the proportion A : B = C : X for the unknown X.
How is X found?
From A/B = C/X, the calculator computes X = B × C ÷ A.
What do I enter in the Proportion Calculator?
The three known values A, B, and C.
Does the Proportion Calculator send my data to a server?
No — the Proportion Calculator runs entirely in your browser, so the numbers you enter never leave your device.
Worked example
Solve 3/4 = x/20: x = 3 × 20 ÷ 4 = 15.