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Ratio Calculator

Reduce two bounded whole-number ratio parts and allocate one explicitly entered total with auditable proportions, percentages, and boundaries.

Use this result well

Inputs that matter
Two bounded whole-number ratio parts, at least one positive, plus one positive numeric total to allocate
Output to expect
Integer-GCD reduced ratio, allocated A/B amounts and each part’s percentage of the entered total
How it works
Reduces the entered whole parts and partitions only the entered total in that proportion; it does not choose units, quantities, tolerances or rounding
  • Convert source quantities to compatible units and confirm the ratio direction before entering the abstract parts.
  • Apply recipe, formulation, safety, countability and rounding rules outside this arithmetic; the two unrounded allocations reconcile to the entered total.

Choose your path

Built around the job you need to finish

Reduce two bounded whole-number ratio parts and allocate one explicitly entered total in that proportion without choosing units, tolerances or application-specific rounding.

Student reducing and allocating a ratio

Connect integer GCD reduction with proportional shares of a total.

Enter two whole parts and one total, then inspect reduced ratio, part sum, allocations and percentages.

Can reproduce both allocations and verify they add back to the entered total.

Recipe or mix planner

Keep the arithmetic separate from safe ingredients, units and batch rules.

Convert all quantities to compatible units externally, enter the abstract ratio and total, then apply domain rounding outside the tool.

Does not treat a numeric allocation as a recipe, formulation or safety instruction.

Operator with a zero part

Represent 0:n or n:0 without permitting 0:0.

Enter one zero and one positive whole part with a positive total.

Gets a valid zero/full allocation while 0:0 is explicitly rejected.

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Reference & details

How it works

Whole-Part Ratio Reduction

Both entered parts are bounded whole numbers and at least one must be positive. Dividing both by their integer GCD preserves the proportion.

Reduced ratio = entered A/GCD : entered B/GCD

Allocate the Entered Total

Each allocation multiplies the same total by one part divided by the sum of both parts. Percent shares expose the same denominator.

Allocated A = total × A ÷ (A + B)

Application Boundary

The tool does not infer units or decide safe mixing, batch constraints, countability, tolerances or rounding. Apply those rules after reviewing the unrounded allocation.

Updated: August 2026

Example Scenarios

A student reviews an already reduced ratio and verifies both allocations against the same total.

Part A: 3Part B: 4Total: 70

3:4; part A 30; part B 40

A reviewer confirms the integer GCD is 6 and that the proportion becomes 2:3.

Part A: 12Part B: 18Total: 125

2:3; part A 50; part B 75

An operator enters 0:5 and receives zero for A and the full entered total for B, while 0:0 remains invalid.

Common Mistakes to Avoid

Entering quantities with incompatible units

Convert source quantities to compatible units first; a numerical ratio does not perform or validate unit conversion.

Rounding both shares independently too early

Retain the unrounded allocations, then apply one documented rounding/remainder rule so the final parts still reconcile to the total.

FAQ

The reducer uses an integer greatest common divisor. Convert compatible decimal quantities to an equivalent whole-number ratio before entry.

Yes. A 0:n or n:0 ratio produces a zero/full allocation. The undefined 0:0 ratio is explicitly rejected.

Yes before display or application-specific rounding. Both allocations use the same entered total and part sum, so their unrounded values reconcile to that total.

No. Convert both source quantities to compatible units and confirm ratio direction outside the calculator before entering the abstract parts.

Only after applying the domain's units, tolerances, safe ingredients, minimum quantities, countability and rounding rules. The calculator provides arithmetic, not a recipe or approval.

About Ratio Calculator

Enter two whole-number ratio parts and one positive total to see the integer-GCD reduction and unrounded proportional allocation.