Ratio Calculator
Use this calculator to simplify ratios, solve a missing value in a proportion, and split a total using a ratio.
1) Simplify a ratio
2) Solve a proportion (A:B = C:D)
Enter any 3 values and leave exactly 1 blank. The calculator will solve for the missing term.
3) Split a total by ratio
Example: Split 500 in the ratio 2:3.
Quick answer: doing ratios on a calculator
If you only need the fast method, here it is:
- To simplify a ratio A:B, divide both numbers by their greatest common factor (GCF).
- To solve A:B = C:x, use cross multiplication: x = (B × C) ÷ A.
- To split a number in ratio A:B, calculate total parts A + B, then do:
- First share = Total × A ÷ (A + B)
- Second share = Total × B ÷ (A + B)
You can do all three with any basic calculator as long as you follow the order carefully.
What a ratio means
A ratio compares two quantities. For example, 3:5 means “for every 3 of one thing, there are 5 of another.” Ratios are used in recipes, exam score comparisons, maps, business analysis, and finance.
A ratio is not always a fraction, but it behaves like one mathematically. That is why you can solve ratio problems by multiplying and dividing.
Method 1: simplify a ratio step by step
Example: simplify 24:36
- Find the GCF of 24 and 36, which is 12.
- Divide both terms by 12:
- 24 ÷ 12 = 2
- 36 ÷ 12 = 3
- Final ratio: 2:3
If your calculator does not have a GCF function, just test common factors (2, 3, 4, 6, etc.) until both numbers divide cleanly.
What if decimals are involved?
Suppose the ratio is 1.5:2.5. Multiply both by 10 first to remove decimals: 15:25, then simplify to 3:5. The calculator at the top does this automatically.
Method 2: solve a missing value in a proportion
When two ratios are equal, they form a proportion. Example:
4:7 = 20:x
Use cross multiplication:
- 4x = 7 × 20
- 4x = 140
- x = 140 ÷ 4 = 35
So 4:7 = 20:35.
On a calculator, this is just two operations: multiply then divide. The key is putting the right values in the right places.
Method 3: divide an amount by ratio
Example: divide $900 in the ratio 2:7
- Total parts = 2 + 7 = 9
- Value of one part = 900 ÷ 9 = 100
- First share = 2 × 100 = 200
- Second share = 7 × 100 = 700
Check: 200 + 700 = 900. Perfect.
This method is useful for splitting costs, revenue shares, inheritance planning, and group contributions.
How to convert a ratio to a percentage
For ratio A:B, the percentage share of A is:
A ÷ (A + B) × 100
For B, it is:
B ÷ (A + B) × 100
Example for 3:5:
- A share = 3 ÷ 8 × 100 = 37.5%
- B share = 5 ÷ 8 × 100 = 62.5%
Common mistakes to avoid
- Only dividing one side when simplifying. You must divide both terms by the same number.
- Mixing up cross multiplication in proportion problems.
- Forgetting to add ratio parts before splitting a total.
- Rounding too early in multistep calculations. Round only at the end.
- Using inconsistent units (for example, meters vs centimeters) without conversion first.
Practice examples you can try now
1) Simplify
48:60 → answer should be 4:5.
2) Solve proportion
6:11 = 30:x → x = 55.
3) Split by ratio
Split 1,200 in ratio 1:2 → 400 and 800.
Use the calculator above to check each result instantly.
Final takeaway
If you remember just three calculator patterns, you can solve nearly all ratio questions:
- Simplify with common factors.
- Use cross multiplication for missing terms.
- Use total parts to split amounts.
Master these and ratio questions become fast, predictable, and easy to verify.