This linear interpolation calculator takes the figures you already have and applies the relationship behind linear interpolation calculations for you, giving intercept abs, m and b from x₁, x₂, x₃, y₁, y₂ and y₃.
What Is the Linear Interpolation Calculator?
The linear interpolation calculator works through x₁, x₂, x₃, y₁, y₂ and y₃ to give you intercept abs, m and b.
It is aimed at the case where you know the method but not the arithmetic: schoolwork, a quick check on a worked example, or a figure that needs to be right first time.
How the Linear Interpolation Works
Each step is applied in order and depends only on the values before it, which makes it possible to follow the calculation rather than take it on trust.
If you are working through the same problem by hand afterwards, compare the intermediate values. That is where a mistake usually shows itself.
Checking Your Own Working
Round sensibly as you go and keep the full precision in the calculator. Rounding too early is the most common way of getting a right method to give a wrong answer.
Where a result should be a whole number, such as a count, check it against the constraint that produced it. A fraction of a person is a sign that something upstream needs revisiting.
A Worked Example
Working through an example, with x₁ set to 10, x₂ set to 5, x₃ set to 2, the calculator returns m of 18, and b of -80, and intercept abs of 80. Substitute your own figures and the same steps produce the same kind of answer.
Frequently Asked Questions
What do I need to work out intercept abs?
Enter x₁, x₂, x₃, y₁, y₂ and y₃. The calculator then works through the relationship and reports intercept abs, m and b.
What does the linear interpolation actually calculate?
It takes x₁, x₂, x₃, y₁, y₂ and y₃ and converts them into intercept abs, m and b using the standard relationship for this problem. Each step is applied in turn, so every output is traceable back to the numbers you typed in.
How should I enter x₁?
Use the value you actually have, in the unit shown next to the field. Enter every value in the same unit system. The calculator assumes the figures you supply are consistent, so it cannot correct a mistake that happens before the calculation starts.
Why does a small change in one value move the answer so much?
That happens when an output depends on a ratio, because dividing by a small number magnifies any change in it. Check the units first, then check whether the value you entered is in the range the relationship was designed for.
Does anything you type get stored?
No. The whole calculation runs inside your browser, and nothing you enter is uploaded, logged or sent anywhere.