One-Sample T-Test Calculator

Where it is used

• Teachers: A teacher pastes in this term's class test scores and checks whether the class average is really different from the national pass mark of 70.
• Cafe and small-business owners: A cafe owner enters 30 order wait times and checks whether the average is different from the 5-minute service they promise on their sign.
• HR and staff-survey teams: An HR officer enters staff satisfaction scores and checks whether the average sits above or below the company target of 8 out of 10.

What the one-sample t-test does

It compares the mean of a single sample against a specific value (for example, testing whether average satisfaction differs from a target of 50). A p-value below 0.05 indicates a statistically significant difference.

When should you use it?

Use it when you have one group of numbers and a single target you want to compare their average against. The numbers should measure the same thing, such as scores, minutes, or ratings, taken from different people or items. It answers questions like whether your average sits above or below a benchmark. Do not use it to compare two separate groups against each other, as that needs a two-sample test. You also need real numbers, not yes or no answers or categories.

What does the result mean?

The main number to read is the p-value. It sits between 0 and 1 and tells you how likely it is that the difference you see is just random luck. A widely used rule is that a p-value below 0.05 means the difference is statistically significant, so your average is probably genuinely different from the target. A value above 0.05 means the evidence is weak, so you cannot be confident there is a real difference. The calculator also shows your sample average, so you can see which way the gap points.

Mistakes to avoid

Do not read a significant result as proof the difference is large or important; it only means the gap is unlikely to be chance. Very small differences can look significant when you have lots of numbers. Make sure every value is really a number, because blank cells or text will throw off the average. Do not mix two different groups in one box. Remember the target is a fixed number you decide beforehand, not another set of data. Finally, a handful of readings can give an unreliable answer.

How to use this calculator

1. Paste or type all your measured numbers into the data box, separating each one with a comma or a new line.
2. Type your single target number, the benchmark you want to compare the average against, into the target box.
3. Press the calculate button to see your sample average and the p-value.
4. Read the p-value: below 0.05 means your average is probably really different from the target, while above 0.05 means you cannot be sure.

Worked example

A cafe promises that orders arrive in 5 minutes. The owner times 30 orders and the average comes out at 5.6 minutes. Putting those 30 times in the data box and 5 in the target box gives a p-value of about 0.01. Because that is below 0.05, the extra wait is a real difference, not just a fluke, so orders really are taking longer than promised.

Frequently asked questions

Related calculators

• T-Test Calculator (Two Samples)
• Paired T-Test Calculator
• Confidence Interval Calculator (Mean)