Linear Interpolation Calculator

How to use

1. 1Pick a mode at the top: Find y from x, Find x from y, Map range, or Bilinear.
2. 2Enter the two known points (or the rectangle corners for bilinear). Fields accept decimals, signed numbers, and simple fractions like 3/4.
3. 3Enter the target value (the x, y, or input value) and read the interpolated result with the slope, normalized parameter t, and a step-by-step derivation.
4. 4Use Map range when you need to remap a sensor reading or a 0..1 number to a different scale, and toggle Clamp to keep the output inside the chosen bounds.
5. 5Click any Copy button to grab the result on its own or the full report with formula, intermediate values, and steps for sharing or pasting into a doc.

About this tool

Linear Interpolation Calculator handles the four problems searchers actually mean when they look up linear interpolation. Find y from x reads a value from a straight line between two known points using y = y1 + (x - x1)(y2 - y1)/(x2 - x1). Find x from y is the inverse and is useful when you know the desired output of a linear sensor or a lookup table and want to back-solve the input. Map range remaps a value from an input range to an output range, which is the same lerp written in the Arduino map and Math.Lerp form, with an optional clamp to the output bounds for safe use in audio, animation, and graphics code. Bilinear interpolation works on a rectangle defined by (x1, y1) and (x2, y2) with corner values Q11, Q21, Q12, and Q22, returning the smooth value at any (x, y) using the standard f(x, y) = (1 - tx)(1 - ty) Q11 + tx (1 - ty) Q21 + (1 - tx) ty Q12 + tx ty Q22 formula that lookup tables, image sampling, climate grids, and finite element interpolation rely on. Every mode reports the slope, the normalized parameter t (or tx and ty), the intercept, and the underlying step-by-step derivation so the result is auditable. Inputs accept integers, decimals, European comma decimals, simple fractions like 3/4, and signed numbers, so engineering tables, scientific data, and code snippets paste in cleanly. When the target lies inside the known range the result panel labels the answer as interpolation, and when it falls outside the panel labels it extrapolation, so you never confuse one for the other. Result precision is configurable up to 12 decimals for copying into spreadsheets, code, or lab reports. Everything runs locally with IEEE 754 double precision in your browser, so the numbers you paste here are never uploaded.

Free to use. Works in your browser. No signup, no login.