What is a ratio calculator?
A ratio compares quantities, for example 1 : 7. This ratio calculator has four tabs: it solves A : B = C : D and A : B : C = D : E : F when values are missing, simplifies ratios to their lowest terms, checks whether ratios are equal, and scales a ratio up or down. Every answer comes with a clear step-by-step solution.
How to use this calculator
- Choose a tab: A:B = C:D, A:B:C = D:E:F, Scale A:B or Scale A:B:C.
- Enter your values. Leave empty the box you want to find, or enter every value to check if two ratios are equal.
- To simplify a ratio, enter only A and B (or A, B and C on the three-term tab).
- On the Scale tabs, choose Multiply or Divide, then type the number to scale every term by.
- Press Calculate, then read the solution and copy it or download it as a PDF.
Ratio formula
A : B = C : D → A × D = B × C
Two ratios are equal when their cross products are equal. To find a missing value, multiply the two known values that sit diagonally and divide by the remaining one. To scale a ratio, multiply or divide every term by the same number.
Solved example
Find X in 1 : 7 = 9 : X. Since 7/1 = X/9, multiplying both sides by 9 gives X = 9 × (7/1) = 63, so 1 : 7 = 9 : 63. Multiplying 1 : 7 by 3 gives 3 : 21.
Frequently asked questions
What is a ratio calculator?
A ratio calculator compares quantities and solves ratio problems for you. Enter your values and it finds a missing value, simplifies a ratio, checks if two ratios are equal, or scales a ratio up or down, with every step shown.
How do I calculate a ratio?
Write the two quantities as A : B, then divide both numbers by their greatest common divisor to reach the simplest form. For example, 12 : 18 simplifies to 2 : 3 because both numbers divide by 6.
How do I find a missing value in a ratio?
Use the A:B = C:D tab. Enter three values, leave the unknown box empty and press Calculate. The calculator cross multiplies the known values and divides by the remaining one. For 1 : 7 = 9 : X the answer is X = 63.
How do I simplify a ratio?
Enter only A and B, or only A, B and C on the three-term tab. The calculator finds the greatest common divisor of the numbers and divides every term by it, so 4 : 6 : 8 becomes 2 : 3 : 4.
How do I check if two ratios are equal?
Fill in all the boxes on the A:B = C:D tab or the A:B:C = D:E:F tab. Two ratios are equal when their cross products are equal, and the calculator shows the cross products and answers True or False.
What is the difference between a ratio and a proportion?
A ratio compares two or more quantities, such as 3 : 4. A proportion is a statement that two ratios are equal, such as 3 : 4 = 6 : 8. A ratio calculator works with both.
How do I scale a ratio up or down?
Open the Scale A:B or Scale A:B:C tab, enter the ratio, choose Multiply or Divide, and type the number. Every term is multiplied or divided by that number, so 1 : 7 multiplied by 3 gives 3 : 21.
How do I solve a three-term ratio like A:B:C = D:E:F?
Use the A:B:C = D:E:F tab. Enter at least one value in each column and one complete pair, for example 1 : 2 : 3 = 4 : X : Y. The scale between the two ratios is found from the complete pair, and the missing values follow.
Can I use decimals or fractions in the ratio calculator?
Yes. You can enter whole numbers, decimals such as 0.5, or fractions such as 1/2 in any box, and the calculator converts them before solving.
Is this ratio calculator free, and can I save the result?
Yes, it is free to use with no sign-up. Each answer comes with a step-by-step solution that you can copy to the clipboard or download as a PDF.