Direct Proportion Calculator
Find a fourth value when two quantities vary in direct proportion. Processing takes place locally in your browser.
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Direct Proportion Calculator
Solves a direct proportion a:b = c:x with x = b times c divided by a and displays the substituted formula plus the rounded result.
All three supplied values must be finite and greater than zero. Decimal precision must be a whole number from 0 through 12.
Verified example: if 3 items cost 12, then 5 items at the same unit rate cost x = 12 times 5 divided by 3 = 20.
The method assumes both quantities change at one constant rate and the units on corresponding sides match. It does not add fixed fees, tiers, discounts or nonlinear effects.
Browser floating-point and requested rounding apply. For prices, medication, engineering, tax or legal quantities, verify the model, units and rounding rule independently.
Output uses a decimal point; very large results may use scientific notation. Floating-point rounding can display a very small positive result as zero. Results beyond the numeric range are rejected. Changing inputs, errors and clear reset the x preview to “?”; calculate again to update it.
Processing takes place locally in your browser.