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Percentage Toolkit

Three percentage calculators in one: find X percent of Y, the percentage difference between two values, and the percentage error of a measurement. Switch tabs and get instant answers.

Result—

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This page replaces the individual converters below, which remain available as standalone pages.

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The three modes

X% of Y answers everyday percent problems like tips, discounts and tax (20% of 150 = 30). Percentage difference compares two values symmetrically — order does not matter. Percentage error measures how far a measurement is from the true value, the standard in science and engineering.

Difference vs change

Percentage difference divides by the average of the two values, so it is symmetric. Percent change (or increase/decrease) divides by the starting value instead, so direction matters. This toolkit uses the symmetric difference formula.

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Percentage Toolkit FAQs

What is the formula for X% of Y?
Multiply Y by X divided by 100. For example, 20% of 150 = 150 × 0.20 = 30.
How is percentage difference calculated?
Absolute difference divided by the average of the two values, times 100: |V1−V2| / ((V1+V2)/2) × 100.
What is percentage error used for?
It quantifies measurement accuracy: |measured − true| / |true| × 100. Lower is better; 0% means a perfect measurement.
Can I use decimals and negatives?
Yes. All three calculators accept decimals, negatives and very large numbers.
Is anything I type stored?
No. All math runs locally in your browser; nothing leaves your device.
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