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Linear Interpolation Calculator

Our Linear Interpolation Calculator helps you find an unknown value (Y) that lies between two known data points (X1, Y1) and (X2, Y2), given a specific X-value. It's a straightforward way to estimate intermediate values in a dataset.

The x-coordinate of your first known point.

The y-coordinate of your first known point.

The x-coordinate of your second known point.

The y-coordinate of your second known point.

The x-coordinate for which you want to find the estimated Y value.

How it works

Our Linear Interpolation Calculator helps you find an unknown value (Y) that lies between two known data points (X1, Y1) and (X2, Y2), given a specific X-value. It's a straightforward way to estimate intermediate values in a dataset.


The Formula
The formula for linear interpolation is:
Y = Y1 + ( (X - X1) * (Y2 - Y1) / (X2 - X1) )

Worked Example
  1. Estimating Temperature

    Suppose you have temperature readings: at 1 PM (X1=1, Y1=20°C) and at 3 PM (X2=3, Y2=24°C). You want to estimate the temperature at 2 PM (X=2). Using the formula: Y = 20 + ((2 - 1) * (24 - 20) / (3 - 1)) = 20 + (1 * 4 / 2) = 20 + 2 = 22°C.


Tips, Assumptions & Limitations
  • Ensure your X-values (X1 and X2) are distinct; if X1 equals X2, interpolation isn't possible.
  • The X value you want to interpolate for should ideally be between X1 and X2 for the most accurate results.
  • Linear interpolation assumes a straight-line relationship between your data points.
FAQ

Linear interpolation is a method of estimating a value that lies between two known data points. It assumes a straight-line relationship between these points to find the intermediate value.

You should use linear interpolation when you have a set of data points and need to estimate a value for an x-coordinate that falls within the range of your known x-coordinates. It's useful for filling in missing data, smoothing curves, or making predictions where a linear trend is reasonable.

While the formula can technically calculate values outside the range of X1 and X2 (extrapolation), linear interpolation is generally less reliable for extrapolation. The further you go beyond your known data points, the less likely the linear assumption holds true, and your estimates may become inaccurate.

Companion article

Linear Interpolation Explained: Estimate Values Between Data Points

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