What you’ll learn
Calculate percent error.
Key idea
Find the absolute difference so the error is nonnegative, divide by the accepted value, then multiply by 100 percent. The accepted value is the reference whole.
If an estimate is 47 when the accepted value is 50, the absolute error is 3. The ratio 3/50 equals 0.06, or 6%. A negative sign does not mean negative error; direction can be described separately as an overestimate or underestimate.
Worked example
Enter the exact value or ordered values in the format requested below.
Accepted length is 20 cm and measured length is 28 cm. Enter the numerical absolute percent error using accepted length as base; omit %.
- The absolute deviation is |28-20|=8 cm.
- Percent error uses accepted reference: 8/20×100=40% regardless of whether measured is above or below.
Answer: 40
Quick Check
Evaluate a worked attempt at calculate percent error, identify the first invalid step, and provide the correction.
Accepted length 40 cm, measured 28 cm. Step 1, absolute deviation=12 cm. Step 2, percent error=(12/28)×100=300/7%. Locate the first invalid step and correct it.