Unit & Ratio Calculator
Solve A : B = C : ?, scale a ratio by N, and convert length, mass and volume units with exact standard factors.
How to use
- Choose a mode at the top — proportion or unit conversion.
- Proportion: fill in A, B and C, pick the value to solve, and the last one is filled in for you.
- Add a scale factor (× N) to see the same ratio multiplied by N.
- Unit conversion: pick a unit group, the from and to units and a value to get the result plus a full unit table.
FAQ
How do I get the height for a 16:9 screen?
Tap 16:9 under ‘Screen ratio’ and enter the width in pixels as C: D is the height. 1920 wide gives 1080, 1280 wide gives 720. To get the width from the height, set the value to solve to C and enter the height as D.
How is the proportion solved?
In A : B = C : D the inner product equals the outer product (A×D = B×C), so the missing value follows from the other three.
Are the conversion factors exact?
Yes. They are the defined standard values, such as 1 inch = 25.4 mm and 1 pound = 453.59237 g.
Which volume units are used?
fl oz and gallon are US units. One US gallon is 3.785411784 L, and one cup is taken as 240 ml.
Which tonne is used?
The metric tonne of 1,000 kg.
How do I convert inches to centimetres?
One inch is exactly 2.54 cm. Pick Length → in → cm: 27 inches is 68.58 cm. Screen sizes in inches measure the diagonal.
How do I convert kilograms to pounds?
One pound is exactly 0.45359237 kg, so 1 kg is about 2.20462 lb and 70 kg is about 154.32 lb.
Can I scale a recipe with it?
Yes. Put the original servings in A, the amount in B and the new servings in C; D is the amount you need. 300 g for 4 servings becomes 450 g for 6.
How is the simplest ratio found?
Whole-number ratios are divided by their greatest common divisor: 1920 : 1080 becomes 16 : 9. With decimals it is shown as 1 : N.