About Percent Error Calculator
This calculator finds the percent error of a measurement. Enter the measured value and the true value, for example 9.6 and 10, and it reports a 4% error with the steps. It is free, needs no sign-up and runs in your browser, so nothing you enter is uploaded.
Percent error is used in physics, chemistry and engineering labs to say how far an experimental result is from an accepted one. It is the absolute gap divided by the true value, so it is always positive. The true value must not be zero.
A small example: if you measure gravitational acceleration as 9.81 and the reference is 9.8, the error is 0.01 ÷ 9.8 × 100 = 0.102%, which the tool rounds as 0.102041%. Many teachers ask for two or three significant figures, so round to suit your course.
How to use Percent Error Calculator
- Choose the mode that matches your question, for example "X% of Y" or "% change".
- Fill in the fields. Each field is labelled in the sentence, such as "Percent" and "Number".
- Each mode opens with a worked example already filled in; change the numbers and the answer updates as you type, with no calculate button.
- Open the working underneath to see the formula and each step of the arithmetic.
- For a discount or a tip, leave the optional tax or people field empty to ignore it.
- If a field would make the sum impossible, such as a zero whole, the calculator tells you which one instead of showing a wrong number.
Features
- Sixteen modes in one place, from percent of a number to a tip split.
- Formula and step-by-step arithmetic shown for every answer.
- Percentage change measured against the absolute starting value, so a negative start still gives a sensible direction.
- Percentage difference that treats both values equally, kept separate from percentage change.
- Reverse percentage for finding the original price or total.
- Discount mode with optional sales tax applied after the discount, plus the amount you save.
- A margin and markup mode that shows profit, margin on price and markup on cost side by side.
- Percent error for lab work and marks percentage for exam results, with marks lost.
- Fraction to percent, percent to fraction and percent to decimal conversions, with fractions reduced to lowest terms.
- Tip calculator with an optional number of people to split the total.
Percent error formula
The size of the error divided by the true value.
error % = |measured − true| ÷ |true| × 100Worked examples
Measured 9.6, true 10 gives 4%
|9.6 − 10| = 0.4, and 0.4 ÷ 10 × 100 = 4.
Measured 9.81, true 9.8 gives 0.102041%
|9.81 − 9.8| = 0.01, and 0.01 ÷ 9.8 × 100 = 0.102041.
Privacy: how it works
- Everything is calculated by code running in your browser tab. The numbers you enter are not sent to Ulkaa or to any other server, and there is nothing to sign in to.
Tips
- Percentage change cannot start from zero, since there is no base to measure against. The calculator says so rather than showing infinity.
- To add or take off a percentage in one step, multiply by 1 plus or minus the decimal. Adding 15% is × 1.15 and taking off 15% is × 0.85.
- Percent points and percent are not the same thing. A rate moving from 10% to 12% is up 2 percentage points but up 20% in relative terms.
- Results keep ten significant figures, so a very small value such as 0.0000042 is not rounded to zero. For money, round the final figure to your currency.
Frequently asked questions
Is it really free?
Yes. There is no price, no trial and no credit card. Ulkaa Tool does the work with your own device, so there is no server bill to pass on to you.
Do I need an account?
No. There is no sign-up and no login. Open the page and use it. An Ulkaa account is not needed for anything on this tool.
Does it run in my browser?
Yes. Your numbers are processed by code running in your browser tab, on your own device.
Is my data uploaded?
No. Your numbers are never sent to Ulkaa or to anyone else. You can check this yourself by watching the Network tab in your browser developer tools while you use the tool.
How do I calculate percent error?
Subtract the true value from the measured value, take the absolute value, divide by the true value and multiply by 100.
Can percent error be negative?
In the usual form it cannot, because the absolute value is taken. Some courses keep the sign to show over or under; if yours does, read the sign from measured minus true.
More Percentage Calculator pages
- Percentage CalculatorPick the question you are asking, enter two numbers and see the answer with its formula.
- What Is X Percent of Y?Enter a percent and a number to get that share of it.
- X Is What Percent of Y?Enter a part and a whole to see the part as a percentage.
- Percentage Increase CalculatorFind how much a value went up, as a percentage of where it started.
- Percentage Decrease CalculatorFind how much a value fell, as a percentage of where it started.
- Percentage Change CalculatorFind the change between two values as a share of the starting value.
- Percentage Difference CalculatorCompare two values that are equals, with no before or after.
- Add a Percentage to a NumberIncrease any number by a percent and get the new total.
- Subtract a Percentage From a NumberReduce any number by a percent and get what is left.
- Reverse Percentage CalculatorWork backwards from a part and its percent to the whole.
- Discount CalculatorEnter a price and a percent off to see what you pay and what you save.
- Marks Percentage CalculatorEnter the marks you scored and the total to get your percentage.
- Fraction to Percent CalculatorEnter a numerator and a denominator to get the percent.