Ratio Calculator

Simplify and solve ratios

In simplify mode, enter two terms and the calculator reduces them using the greatest common divisor — turning 16:9 or 1920:1080 into their simplest form. In proportion mode, fill in three of the four values in A:B = C:D and leave one blank to solve for it, perfect for scaling recipes, maps and mixtures.

Two modes

• Simplify a ratio to lowest terms
• Solve a proportion for the unknown value
• See decimal and fraction equivalents

Key features at a glance

• Simplify a ratio to its lowest whole-number terms
• Solve a proportion A:B = C:D for the missing value
• Uses the greatest common divisor for exact simplification
• Shows decimal and fraction equivalents
• Handles common cases like aspect ratios instantly
• Runs entirely in your browser, even offline

How ratios are simplified

Simplifying a ratio means reducing both terms to the smallest whole numbers that preserve the same relationship. The method is to find the greatest common divisor (GCD) of the two terms — the largest number that divides both exactly — and divide each term by it. A ratio of 1920:1080, for instance, has a GCD of 120, which reduces it to the familiar 16:9 aspect ratio.

This is the same logic used to reduce fractions, because a ratio and a fraction express the same proportional relationship. Simplifying makes ratios easier to understand and compare: 16:9 is instantly recognizable as a widescreen shape, whereas 1920:1080 is not. The calculator computes the GCD for you and presents the reduced form along with decimal and fraction equivalents.

Solving proportions for a missing value

A proportion states that two ratios are equal, written A:B = C:D. When three of the four values are known, you can solve for the fourth using cross-multiplication: A times D equals B times C. Rearranging gives the unknown — for example, if 2:5 = x:20, then x = (2 × 20) ÷ 5 = 8. The calculator handles this automatically when you leave one field blank.

Proportions are one of the most practical tools in everyday math. They underlie scaling a recipe up or down, converting between units, reading a map's scale, mixing solutions to a given strength, and resizing images while keeping their shape. Anytime you need to keep one relationship constant while changing the numbers, a proportion is the right model, and solving for the unknown is exactly what this mode does.

Ratios, fractions, and aspect ratios

Ratios, fractions, and decimals are three views of the same proportional idea, which is why the calculator shows all of them. The ratio 3:4 is the fraction 3/4 is the decimal 0.75. Being able to flip between forms is handy because different contexts prefer different representations: recipes and odds use ratios, math problems use fractions, and measurements often use decimals.

Aspect ratios are a particularly common use. Screens, photos, and videos are described by ratios like 16:9, 4:3, or 1:1, and simplifying a pixel dimension to its aspect ratio — or scaling a known aspect ratio up to a target width — is a frequent task for designers and photographers. The simplify and proportion modes together cover both directions of that work.

Tips for working with ratios

• Simplify pixel dimensions to identify an aspect ratio like 16:9
• Use proportion mode to scale recipes, maps, and mixtures
• Leave exactly one field blank to solve a proportion
• Check the decimal form to compare two ratios quickly
• Remember a ratio, its fraction, and its decimal are the same relationship

Why choose our ratio calculator?

Our calculator is completely free with no signup, no limits, and no subscription. It runs entirely in your browser, so results are instant, it works offline, and your numbers never leave your device.

It is one of more than 200 free tools on ToopTools, and you can pin it to your My Workspace, a personalized workspace where you keep the tools you use most in a single dashboard. Beside the fraction and percentage calculators, it covers every proportional calculation in one place.

Common use cases

People use the ratio calculator to simplify ratios, identify aspect ratios from pixel dimensions, and scale recipes, paint mixes, and chemical solutions up or down while keeping proportions correct. Students use it for proportion problems in math and science homework.

Designers and photographers use it to work with aspect ratios when cropping and resizing, and anyone splitting something in a given ratio — like sharing costs or ingredients — uses it to find the exact amounts. The two modes cover both simplifying an existing ratio and solving for an unknown.

Is the ratio calculator free?

Yes. It is completely free with no account, no sign-up, and no usage limits. Simplify and solve as many ratios as you like at no cost.

How do I simplify a ratio?

Divide both terms by their greatest common divisor. The calculator does this automatically, reducing a ratio like 1920:1080 to its simplest form, 16:9, and showing the decimal and fraction equivalents.

How do I solve a proportion?

Enter three of the four values in A:B = C:D and leave one blank. The calculator cross-multiplies to find the missing value, so 2:5 = x:20 gives x = 8.

Can I use it for aspect ratios?

Yes. Enter a width and height, such as 1920 and 1080, and simplify mode returns the aspect ratio, 16:9. You can also scale a known aspect ratio to a target dimension using proportion mode.

Does it show fractions and decimals too?

Yes. Alongside the simplified ratio, the calculator displays the equivalent fraction and decimal, so you can use whichever representation suits your task.

Are my calculations private?

Yes. Everything is computed in your browser and nothing is uploaded, so your numbers stay private and the tool works without an internet connection.

How do I scale a ratio up or down?

Enter the known parts of your ratio and leave the unknown value blank — the calculator solves the proportion and fills it in, keeping the ratio in balance. This makes it easy to scale a recipe, mixture, or design up or down to a new size.

Does the ratio calculator work offline?

Yes. The calculation runs entirely in your browser, so once the page has loaded the tool works without an internet connection, and nothing you enter is uploaded — it stays private on your own device.