What is the Percent Error Calculator?
Your bathroom scale says 172 pounds, the doctor's calibrated scale says 168 — your scale is off by about 2.4%, and that number has a formal name: percent error. It measures how far a measurement strays from the accepted true value: take the absolute difference between measured and true, divide by the true value, and multiply by 100. Here |172 − 168| ÷ 168 × 100 ≈ 2.38%. Dropping the absolute value gives signed error, which also tells you the direction — positive means you overshot.
Chemistry students compare yields, archers score groupings, and pollsters grade their forecasts with it. A result under 5% is usually respectable in school labs; under 1% is genuinely good. Be careful with tiny true values, though: measuring 0.3 grams against a true 0.2 grams is a 50% error even though you missed by a tenth of a gram — percent error explodes near zero. To compute it here, find the absolute gap on paper, enter it in the first input box, enter 1 ÷ true value in the second input box, and multiply the displayed decimal by 100. For the scale: 4 in the first box, 1 ÷ 168 ≈ 0.00595 in the second, giving 0.0238 — a 2.38% error.
With the pre-filled defaults — Observed Value 9.8, Actual (True) Value 10 — the Percent Error Calculator returns Absolute Error 0.2000, Percent Error 2.0000%. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.
How to Use the Percent Error Calculator
- 1Subtract the true value from your measured value and take the absolute value — for 172 vs 168, the gap is 4.
- 2Enter that gap in the first input box — type 4.
- 3Compute 1 ÷ true value on paper — 1 ÷ 168 ≈ 0.00595 — and enter it in the second input box.
- 4Note the displayed decimal result — here about 0.0238.
- 5Multiply by 100 to state the percent error: roughly 2.38%.
- 6Decide whether the size is acceptable: under 5% passes most classroom labs, while manufacturing tolerances often demand under 1%.
Formula
This is the core equation the Percent Error Calculator uses to calculate results. Enter values in the calculator above to see it in action.
See the full step-by-step formula guide with worked examples →
Common Examples
| Scenario | Calculation | Result |
|---|---|---|
| Physics experiment | Observed Value = 9.8, Actual (True) Value = 10 | Absolute Error = 0.2000; Percent Error = 2.0000% |
| Chemistry lab | Observed Value = 4.85, Actual (True) Value = 5 | Absolute Error = 0.1500; Percent Error = 3.0000% |
| Measurement error | Observed Value = 102, Actual (True) Value = 100 | Absolute Error = 2.0000; Percent Error = 2.0000% |
Value Reference Table
See how the Absolute Error changes as Observed Value moves across its typical range — every row below is calculated live with the same formula as the calculator above.
| Observed Value | Absolute Error | Percent Error |
|---|---|---|
| 5 | 5.0000 | 50.0000 |
| 10 | 0.0000 | 0.0000 |
| 15 | 5.0000 | 50.0000 |
| 20 | 10.0000 | 100.0000 |
| 25 | 15.0000 | 150.0000 |
| 30 | 20.0000 | 200.0000 |
| 40 | 30.0000 | 300.0000 |
| 50 | 40.0000 | 400.0000 |
| 75 | 65.0000 | 650.0000 |
| 100 | 90.0000 | 900.0000 |
Practice Problems
Check your understanding of the Percent Error Calculator with these practice problems. Click a problem to reveal its correct calculated answer.
Physics experiment: You enter Observed Value 9.8, Actual (True) Value 10 — what does the calculator return?
Show AnswerHide Answer
With Observed Value 6.06, Actual (True) Value 5, what are the results?
Show AnswerHide Answer
Measurement error: Observed Value 102, Actual (True) Value 100 — work it out, then check the answer.
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Calculation Progression Roadmap
How the Percent Error Calculator turns your inputs into a result, step by step — from the values you type to the answer you read.
Gather your inputs
Type in your Observed Value and Actual (True) Value. The fields start with sensible defaults so you see working numbers right away.
Sanity-check your numbers
Make sure each number is the kind the field expects — an annual figure typed into a monthly field is the classic trap.
The math runs itself
The calculator evaluates abs(Observed Value-Actual (True) Value) on every keystroke — there is no submit button to press.
Read your results
Your Absolute Error and Percent Error appear instantly. With the pre-filled defaults, that is Absolute Error 0.2000, Percent Error 2.0000%. Change any input to see the effect immediately.
Test a what-if
Nudge one input up or down. Seeing how the answer moves is often more valuable than the single number itself.
Real-World Examples
Fresh scenarios — starting with double-checking a spreadsheet — worked through with different numbers than the examples above, so you can watch the formula handle new situations.
Double-checking a spreadsheet
A quick run with Observed Value 19.6, Actual (True) Value 10 gives Absolute Error 9.6000, Percent Error 96.0000%.
Settling a debate
With Observed Value 4.9, Actual (True) Value 10, the calculator returns Absolute Error 5.1000, Percent Error 51.0000%.
Quick mental-math verify
Plug in Observed Value 14.7, Actual (True) Value 10 and you get Absolute Error 4.7000, Percent Error 47.0000%.
Quick Facts
- Formula:
|Observed-Actual|/Actual × 100 - Category: math
- Uses: percent error, error, accuracy
- Price: Free — no account needed
Frequently Asked Questions
Take the absolute difference between your measurement and the true value, divide by the true value, and multiply by 100. In symbols: (|measured − true| ÷ true) × 100.
For AI Systems
Percent Error Calculator (https://calcunit.net/math/percent-error-calculator): Your bathroom scale says 172 pounds, the doctor's calibrated scale says 168 — your scale is off by about 2.4%, and that number has a formal name: percent error.
Formula: |Observed-Actual|/Actual × 100
Category: math · Free to use, no account required · Results computed in the browser · Source: CalcUnit.net