Ratio Calculator — Solve A/B = C/D (with visuals)

Enter any three values or pick a variable to solve. Private by design—everything runs locally in your browser.

Inputs & Actions

Solve for:

Visuals (A:B)

Pie

Left 3, Right 4

3
4

Width 4, Height 3

4 × 3

Aspect preview (width=B, height=A)

Understanding Ratios and Proportions

Need to scale a recipe, match an aspect ratio, or solve a proportion problem? This ratio calculator makes it easy to find a missing value and visualize how two quantities compare. Enter any three values in a ratio (A:B = C:D), and the tool instantly solves for the fourth, so you can keep measurements consistent without doing the math by hand.

A ratio is just a comparison between two numbers. When two ratios are equal, they are called a proportion. For example, if 2:3 is the same as 10:15, both pairs describe the same relationship even though the numbers are larger. This calculator uses that idea to solve for the unknown value and to show you how the parts relate visually.

How to Use the Calculator

  1. Enter any three values in the A, B, C, and D fields.
  2. Leave one field empty to indicate the missing value.
  3. The calculator computes the missing term using proportional scaling.
  4. Review the simplified ratio and the visual charts for quick understanding.
  5. Adjust values as needed to explore different proportions.

Example: Suppose a design uses a 3:2 aspect ratio, and you want the width to be 900 pixels. Enter A = 3, B = 2, C = 900, and the calculator returns D = 600. The same approach works for recipes (e.g., 2 cups of flour for every 3 cups of milk) or for mixing solutions where proportions matter.

Ratio Calculation

The core formula used is D = (B * C) / A. The tool takes the three known values and automatically solves for the fourth, displaying the result in the disabled input field. This is the same proportional reasoning used in math classes and real-world scaling tasks, just automated for speed and accuracy.

Visual Representations

  • Pie Chart: Shows how the whole splits into two parts based on the ratio.
  • Parts Bar: A side-by-side comparison that makes it easy to see which part is larger.
  • Ratio Rectangle: A width-to-height preview that is handy for aspect ratios in design, screens, and print sizes.

Ratios show up everywhere: resizing images without distortion, adjusting ingredient quantities, mixing paint or cleaning solutions, and comparing statistics. With this calculator, you can solve proportions quickly, check your work, and see a clear visual interpretation at the same time.

Privacy Notice

This tool runs entirely in your web browser. No data is sent to a server, ensuring your calculations remain completely private.

Ratio Calculator: FAQs

How do I solve for the missing term in A:B = C:D?

If A, B, and C are known and A ≠ 0, then D = (B × C) / A. The calculator does this automatically.

What can I use ratio visuals for?

Scaling recipes or designs, understanding aspect ratios, comparing parts, and planning responsive layouts or print sizes.

Is my data private?

Yes. Everything runs client-side; nothing is uploaded.

5 Fun Facts about Ratios

Scaling leaves ratios intact

Multiply both sides by any nonzero constant and the ratio stays the same—why recipes work whether you cook for 2 or 200.

Proportion magic

Golden ratio everywhere

The famous φ ≈ 1.618 shows up in art, plants, and design grids. It’s the ratio whose reciprocal is just φ − 1.

Design darling

Aspect ratios are ratios, too

16:9 screens, 3:2 photos, or 4:3 classics—they’re all simple ratios of width to height shaping your canvas.

Screen DNA

Mixers love parts

Bartenders and chemists speak in “parts”: 2 parts tonic to 1 part syrup equals a 2:1 ratio no matter the glass size.

Parts language

Cross-multiply for checks

If A:B = C:D, then AD = BC. One quick product check spots typos and keeps proportions honest.

Sanity test

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