⚖️ Ratio Calculator
Solve ratio and proportion problems. Find missing values in A:B = C:D equations.
Leave one field empty to solve for it.
About the Ratio Calculator
This ratio calculator runs entirely in your browser. Enter any three of the four values in a proportion A:B = C:D, leave one blank, and click Solve to find the missing value. Nothing is uploaded — all math happens on your device.
How ratios are solved
A proportion states that two ratios are equal: A:B = C:D. Using cross multiplication, A × D = B × C. To solve for any one missing value:
- Solve for A: A = (B × C) / D
- Solve for B: B = (A × D) / C
- Solve for C: C = (A × D) / B
- Solve for D: D = (B × C) / A
How to use the calculator
- Enter three of the four values (A, B, C, D).
- Leave the field you want to solve for empty.
- Click Solve to see the missing value, the full ratio, and the decimal equivalent.
- Click Clear to reset.
Frequently asked questions
What if I leave more than one field empty? The calculator needs exactly three values to solve for one unknown. Leave exactly one field blank.
What if a value is 0? If the value you're dividing by is 0, the equation has no solution. The calculator will warn you.
Can I use decimals? Yes. All inputs accept decimal values.
Does this tool save my data? No. All calculations happen locally in your browser.