➗ Ratio Calculator
Solve proportions, simplify ratios, split an amount by a ratio and work out aspect ratios — four common ratio jobs on one page.
How to use the ratio calculator
Four everyday ratio jobs live on one page. Results update as you type under each box, and the result panel on the right collects everything so you can copy it in one click.
- Proportion solver — find the missing value in A : B = C : ?. Use it to scale a recipe, read a map scale, or work out "if 3 cost $4, what do 15 cost?"
- Simplify a ratio — reduce 48:36 to 4:3. Decimals (1.5:2.5) and three or more terms (6:4:2) work too.
- Split an amount — divide a total by a ratio such as 60:40 or 5:3:2. Handy for splitting rent, profits, tips or a shared bill.
- Aspect ratio — find the aspect ratio of any resolution and the new height when you resize an image or video without stretching it.
How to solve a proportion
In a proportion A : B = C : D, the product of the outer terms equals the product of the inner terms (A × D = B × C), so D = B × C ÷ A. Cross-multiplying is the same idea. Example: a recipe uses 3 cups of flour for 4 tablespoons of sugar. Scaling up to 15 cups of flour needs 4 × 15 ÷ 3 = 20 tablespoons of sugar.
How to simplify a ratio (GCD)
Divide every term by the greatest common divisor (GCD). The GCD of 1920 and 1080 is 120, so 1920 : 1080 = 16 : 9. If a term has decimals, first multiply every term by a power of ten to make them whole numbers (1.5 : 2.5 → 15 : 25 → 3 : 5). Below the answer you also get the ratio scaled so the first term is 1, and each term as a percentage of the total.
How to split an amount by a ratio
each share = total × (that part ÷ sum of all parts). Splitting $1,000 in a 3:2 ratio: the parts add up to 5, so the shares are $600 (3/5) and $400 (2/5). When the amount does not divide evenly, shares are rounded to the cent and the leftover penny goes to the last share, so the shares always add up to exactly the total.
| Ratio | Percent split | $1,000 becomes |
|---|---|---|
| 1:1 | 50% / 50% | $500 / $500 |
| 3:2 | 60% / 40% | $600 / $400 |
| 7:3 | 70% / 30% | $700 / $300 |
| 2:1 | 66.7% / 33.3% | $666.67 / $333.33 |
| 5:3:2 | 50% / 30% / 20% | $500 / $300 / $200 |
Aspect ratios and screen resolutions
An aspect ratio is the simplified width : height of a screen or image. 1080p (1920×1080), 1440p (2560×1440) and 4K UHD (3840×2160) are all 16:9. "21:9 ultrawide" is a marketing name: 2560×1080 is really 64:27 (≈ 2.37:1) and 3440×1440 is 43:18 (≈ 2.39:1). That is why the calculator also shows width ÷ height and an "≈ n : 9" value.
To resize without distortion, keep the ratio: new height = new width × original height ÷ original width. Scaling a 2560×1440 image to 1280 wide gives 720 tall.
Ratios vs percentages
A 3:2 split means 60% and 40% of the whole — not "3 is 50% more than 2" (although that is also true). Divide a term by the total to get a percentage; divide two terms by each other to get "how many times". For percent change, discounts and markups, the percentage calculator is quicker.
Amount splitting is simple ratio math. For taxes, fees or legal ownership splits, follow your agreement and professional advice.