Ratio Calculator

A ratio compares two quantities by division. The ratio 3:4 means for every 3 units of the first quantity there are 4 of the second. You can write a ratio with a colon (3:4), as a fraction (3/4), or as a decimal (0.75).

Divide both values by their greatest common divisor (GCD). The ratio 12:18 has a GCD of 6, so it simplifies to 2:3. For decimal inputs like 0.4:0.6, the calculator first multiplies both sides by a power of 10 to get whole numbers (4:6), then divides by the GCD to reach 2:3.

Cross-multiply and divide. For a:b = c:d with c unknown, the formula is c = (a x d) / b, so c = (3 x 20) / 4 = 15 and 3:4 = 15:20. In the calculator, fill A and B, enter either C or D, and leave the other blank to solve for it.

Aspect ratio is the width-to-height ratio of a display. A 1920 x 1080 screen has an aspect ratio of 1920:1080, which simplifies to 16:9. Common ratios include 16:9 (widescreen HD), 4:3 (older TVs and monitors), and 21:9 (ultrawide).

Ratios appear in recipes (2 cups flour to 1 cup sugar), map scales (1 inch to 10 miles), car gear ratios, fuel or paint mixing, accounting metrics like the debt-to-equity ratio, and screen or photo aspect ratios.