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Solve A : B = C : D, simplify ratios with decimals or three parts, scale by a factor and size screens to 16:9, 4:3 or 21:9, with the working shown.
Leave one box empty to solve it. Fill all four to check whether the two ratios are equal.
Up to six terms. Decimals such as 1.5 and fractions such as 3/4 work.
Type a width or a height; the other side is worked out.
Type any size, such as a screen resolution, to get its ratio.
Private by design. Everything runs in your browser and nothing is uploaded. Copy link saves your numbers in the address, so you can share them.
A ratio calculator compares quantities written as A : B. It finds the missing term of a proportion such as 3 : 4 = 600 : D (D = 800), reduces a ratio to its simplest whole numbers, scales it by a factor and splits a total in a given ratio. This one also sizes screens to 16:9, 4:3 or 21:9.
A ratio says how many of one thing there are for each of another. 3 : 4 means 3 parts for every 4 parts, so the first quantity is 3/4 (0.75) of the second and takes 3 of the 7 parts, about 42.86% of the total. Two ratios that are equal, like 3 : 4 and 600 : 800, form a proportion.
| Ratio | Simplest | As 1 : n | As n : 1 | Share of total |
|---|---|---|---|---|
| 3 : 4 | 3 : 4 | 1 : 1.3333333333333 | 0.75 : 1 | 42.86%, 57.14% |
| 12 : 18 : 30 | 2 : 3 : 5 | 1 : 1.5 : 2.5 | 0.4 : 0.6 : 1 | 20%, 30%, 50% |
| 1.5 : 2.25 | 2 : 3 | 1 : 1.5 | 0.66666666666667 : 1 | 40%, 60% |
| 16 : 9 | 16 : 9 | 1 : 0.5625 | 1.7777777777778 : 1 | 64%, 36% |
| 250 : 280 | 25 : 28 | 1 : 1.12 | 0.89285714285714 : 1 | 47.17%, 52.83% |
| 1 : 2 : 4 | 1 : 2 : 4 | 1 : 2 : 4 | 0.25 : 0.5 : 1 | 14.29%, 28.57%, 57.14% |
Pick a task. The answer and the working update as you type, with no Calculate button.
Type three of A, B, C and D and leave one box empty. The calculator cross-multiplies and fills it in. Fill all four to check whether the two ratios are equal.
Enter two to six terms. Decimals and fractions are turned into whole numbers first, then every term is divided by the greatest common divisor.
Enlarge or shrink every term by the same factor, or share a total such as 350 in the ratio 3 : 4 (150 and 200).
Choose 16:9, 4:3, 21:9, 16:10 or 9:16 and type a width or a height. Or type any resolution to find its ratio and the closest common format.
Each row is what the calculator does behind the result, in the same order as the working panel.
| Task | Formula | Example |
|---|---|---|
| Missing fourth term | D = B × C ÷ A | 3 : 4 = 600 : D, so D = 4 × 600 ÷ 3 = 800 |
| Missing first term | A = B × C ÷ D | A : 4 = 600 : 800, so A = 4 × 600 ÷ 800 = 3 |
| Check a proportion | A × D = B × C | 3 × 800 = 2400 and 4 × 600 = 2400, so 3 : 4 = 600 : 800 |
| Simplify | Divide every term by the GCD | 12 : 18 : 30, GCD 6, gives 2 : 3 : 5 |
| Simplify decimals | Multiply to whole numbers, then divide by the GCD | 1.5 : 2.25 × 4 = 6 : 9, GCD 3, gives 2 : 3 |
| Unit ratio | 1 : (B ÷ A) or (A ÷ B) : 1 | 3 : 4 = 1 : 1.3333 = 0.75 : 1 |
| Percentage split | A ÷ (A + B) × 100 | 3 ÷ 7 × 100 = 42.857142857143% |
| Scale | Multiply or divide every term by k | 250 : 280 shrunk 2.5 times = 100 : 112 |
| Split a total | Part = total × term ÷ sum of terms | 350 in 3 : 4: one part 350 ÷ 7 = 50, so 150 and 200 |
| Height from width | H = W × ratio height ÷ ratio width | 16:9 at 1920 wide: 1920 × 9 ÷ 16 = 1080 |
An aspect ratio is width : height. Use the Aspect mode above for any size not listed. To keep long numbers tidy, the significant figures calculator rounds them to the precision you need.
| Ratio | Decimal | Example sizes (px) | Where you see it |
|---|---|---|---|
| 1:1 | 1 | 1080 × 1080 | Square photos and social posts |
| 4:3 | 1.333 | 640 × 480, 1024 × 768, 1600 × 1200 | Older TVs and computer monitors |
| 3:2 | 1.5 | 3000 × 2000, 6000 × 4000 | Many camera sensors and photo prints |
| 16:10 | 1.6 | 1280 × 800, 1920 × 1200, 2560 × 1600 | Laptops and office monitors |
| 16:9 | 1.778 | 1280 × 720, 1920 × 1080, 3840 × 2160 | HDTV, 4K, most monitors and online video |
| 1.85:1 | 1.85 | 1998 × 1080 | Widescreen cinema |
| 64:27 (21:9) | 2.370 | 2560 × 1080 | Ultrawide monitors |
| 43:18 (21:9) | 2.389 | 3440 × 1440 | Ultrawide monitors |
| 2.39:1 | 2.39 | about 1920 × 803 | Anamorphic widescreen cinema |
| 9:16 | 0.5625 | 1080 × 1920 | Vertical phone video and stories |
What a typical free ratio calculator offers next to this one.
| Feature | Typical ratio calculator | This calculator |
|---|---|---|
| Results | After pressing Calculate | As you type |
| Solve A : B = C : D | Usually D only, or any one term | Any one term, or check all four |
| Simplify | Two whole numbers | Two to six terms, decimals and fractions |
| Repeating answers | Rounded decimal | Decimal plus the exact fraction, such as 70/3 |
| Split a total in a ratio | Rarely | Yes, with a check that the parts add up |
| Aspect ratios | Separate tool, or a table only | Presets, size from ratio and ratio from size |
| Working | Formula only, or none | Every step with your numbers |
| Percentage split | Sometimes | Every term, with a bar |
| Share your numbers | Rarely | Copy link keeps them in the address |
A recipe uses 2 cups of flour to 3 eggs and you have 5 eggs. Solve 2 : 3 = C : 5 to get 3.33 cups.
A 1 : 2 : 4 concrete mix needs 7 parts in all. Split 140 kg in that ratio to get 20, 40 and 80 kg.
Split a bill or rent in proportion to income or use with Split a total. To track the shared costs over time, use the expense calculator.
On a 1 : 50,000 map, 3 cm is 150,000 cm, or 1.5 km. Solve 1 : 50000 = 3 : D.
Find the height of a 16:9 thumbnail, the width of a 9:16 story, or check that 1366 × 768 is close to 16:9.
The working lists each step, cross-multiplying, finding the GCD and dividing, so you can compare it with your own.
Most ratio mistakes come from order and units. For more maths and everyday tools, see all free online calculators.
3 : 4 and 4 : 3 are different ratios. Keep the terms in the same order on both sides of a proportion.
Compare 50 cm to 2 m as 50 : 200, which is 1 : 4, not 50 : 2.
In 3 : 4 the first part is 3/4 of the second but 3/7 of the whole. The share line shows the part-to-whole view.
A mix such as 1 : 2 : 4 has three. You can simplify, scale and split it the same way.
Ultrawide monitors sold as 21:9 are usually 64:27 (2560 × 1080) or 43:18 (3440 × 1440), close to but not exactly 21:9.
Inputs are kept as exact fractions, so 0.1 : 0.3 = 0.2 : D gives exactly 0.6. Decimals are shown to 14 significant digits.
Proportions with negative numbers are solved, but simplifying, splitting and percentage shares need terms that are zero or positive.
Answers that do not end, such as 70/3, are shown to 14 significant digits with the exact fraction beside them. Pixel sizes are also shown rounded to whole pixels.
It does the arithmetic only. Check mix ratios, doses and ratios used in finance against the guidance that applies to your case.
The definitions and aspect ratio facts on this page come from these references, last checked on November 9, 2026. The arithmetic follows the formulas in the table above.
Short answers to what people ask most. To keep your answers, paste them into the online notepad.
Write the two amounts as A : B in the same units, then divide both by their greatest common divisor. For example, 12 boys and 18 girls is 12 : 18, which simplifies to 2 : 3.
Cross-multiply. In A : B = C : D the products A times D and B times C are equal, so D = B times C divided by A. For 3 : 4 = 600 : D, D = 4 times 600 divided by 3 = 800.
Multiply every term by the same number until all are whole, then divide by the greatest common divisor. 1.5 : 2.25 times 4 is 6 : 9, which simplifies to 2 : 3.
Yes. A concrete mix of 1 : 2 : 4 has three parts. This calculator simplifies, scales and splits ratios of up to six terms.
Divide each term by the sum of all terms and multiply by 100. In 3 : 4 the first part is 3 divided by 7, about 42.86%, and the second is about 57.14%.
Add the terms to get the number of parts, divide the amount by that number, then multiply by each term. 350 in the ratio 3 : 4 is 7 parts of 50, so 150 and 200.
It rewrites the ratio so the first term is 1, by dividing every term by the first. 3 : 4 becomes 1 : 1.3333, and in n : 1 form it is 0.75 : 1.
Multiply or divide every term by the same factor. 250 : 280 divided by 2.5 is 100 : 112, and both simplify to 25 : 28, so the ratio itself does not change.
Height = width times 9 divided by 16, so 1920 times 9 divided by 16 = 1080 pixels. At 1280 wide it is 720, and at 3840 wide it is 2160.
Not usually. Ultrawide monitors sold as 21:9 are mostly 2560 by 1080, which is 64:27, or 3440 by 1440, which is 43:18. Both are close to 21:9 but not equal to it.
1366 by 768 simplifies to 683 : 384, about 1.7786 : 1. That is within 0.05% of 16:9, so it is usually listed as a 16:9 screen.
No. The calculator runs in your browser and nothing is sent to a server. Copy link puts your numbers in the page address only so you can share them.