Quick answerAn average calculator combines a list of values into one representative number. The ordinary arithmetic mean gives every observation equal influence, while a weighted average lets credits, quantities, probabilities, or other weights control how strongly each value contributes.
What the arithmetic mean actually measures
The arithmetic mean is found by adding every value and dividing by the number of values. It is appropriate when each observation represents one comparable unit. A repeated value counts repeatedly; removing duplicates changes the question rather than cleaning the arithmetic. Checking the displayed count and sum is a quick way to catch a number that was skipped or entered twice.
A mean can fall between observed values and does not have to appear in the original list. It also reacts to extreme numbers. If most delivery times are near 30 minutes but one delay lasts four hours, the mean rises sharply. The median shown alongside the result can help reveal when that single center value tells a different story.
When to use a weighted average
Weights are useful when observations represent unequal amounts. A course grade may weight an exam more than a quiz; an investment return may be weighted by dollars invested; and an average unit price may be weighted by quantity purchased. Multiply each value by its matching weight, add those products, and divide by the total weight.
Weights do not have to add to 100. Percentages such as 20, 30, and 50 produce the same weighted average as decimals 0.2, 0.3, and 0.5 because both numerator and denominator scale together. What matters is that every value has one matching nonnegative weight and that their total is greater than zero.
How to use this average calculator
- Paste numbers separated by commas, spaces, or new lines.
- For a weighted average, expand the optional section and enter one nonnegative weight per value.
- Check the count and sum to catch missing or duplicated entries.
Formula and method
Every unweighted value contributes equally. Weighted calculations require one weight for every value and a positive total weight.
Simple and weighted average example
The simple average of 70, 80, and 100 is 250 divided by 3, or about 83.33. That treats all three scores equally. If they are a quiz worth 10 percent, a project worth 30 percent, and an exam worth 60 percent, equal treatment no longer represents the grading plan.
The weighted products are 700, 2,400, and 6,000 when weights are entered as 10, 30, and 60. Their sum is 9,100 and the weight total is 100, producing a weighted average of 91. The difference is not a rounding issue; it comes from asking two genuinely different questions.
Common mistakes to avoid
- Averaging group averages without accounting for different group sizes.
- Entering fewer weights than values.
- Removing repeated observations that are valid parts of the data.
- Using the mean alone when outliers make the median more representative.
Accuracy and practical limits
The calculator retains full numeric precision through the sum and division and rounds only the display. Very large lists or values with vastly different magnitudes can reach ordinary JavaScript floating-point limits. For official grades, financial reporting, or experimental analysis, also confirm the data selection, missing-value policy, and required rounding convention.
Method basis: Standard mathematical definitions and the assumptions stated above. See our editorial and testing standards.
Frequently asked questions
What type of average is shown by default?
The default is the arithmetic mean: the sum divided by the count.
Can a weight be zero?
Yes. A zero weight leaves that value in the entered list but gives it no influence on the weighted result.
Are percentages valid inputs?
Yes, if every value uses the same percentage scale; enter 85 rather than the percent symbol.