Equivalent Ratio Calculator
Solve a missing term in a:b = c:d. Leave exactly one box blank, then check the answer by comparing the two cross-products.
Written and checked by TheToolNet Editorial Team · Last reviewed: September 20, 2026 · Editorial method
Find the missing ratio term
Equivalent ratio formula
For 2:3 = 10:x, cross-multiply to get 2x = 30, then divide by 2. The missing term is x = 15, so 2:3 and 10:15 both equal two thirds.
Scale up or simplify
Multiplying every ratio term by the same nonzero factor makes an equivalent ratio. Dividing every term by a common factor simplifies it. Cross-products provide a direct check even when the scale factor is not obvious.
Frequently asked questions
Can an equivalent ratio contain decimals?
Yes. Equivalent ratios depend on equal quotients, not on whole-number notation.
Why must only one field be blank?
Three known terms determine the fourth. With two unknowns, there are infinitely many possible ratios.
How do I simplify a full ratio?
Use how to calculate ratio for two to eight terms.