Find any y value between two known points instantly
Known Points & Target
Result
30% of the way from x₀ to x₁
Formula
y = y₀ + (x − x₀) × (y₁ − y₀) / (x₁ − x₀)
y = 10 + (30 − 0) × 0.4 = 22
How It Works
A linear interpolation calculator lets you estimate an unknown y value that lies on a straight line between two known data points. Whether you're working with sensor readings, financial data, engineering measurements, or scientific tables, the lerp formula — y = y₀ + (x − x₀) × (y₁ − y₀) / (x₁ − x₀) — gives you an instant, accurate answer without spreadsheets or manual algebra.
Linear interpolation estimates a value between two known data points by assuming a straight-line relationship between them. Given points (x₀, y₀) and (x₁, y₁), the formula y = y₀ + (x − x₀) × (y₁ − y₀) / (x₁ − x₀) finds y for any x.
Interpolation finds a value inside the range of the two known points (x₀ ≤ x ≤ x₁). Extrapolation uses the same formula but extends beyond that range. Extrapolation is less reliable because the data may not actually remain linear outside the known interval.
Common uses include reading between rows in lookup tables, converting between unit scales, estimating temperature or pressure at an intermediate point, and filling in missing data values in engineering or scientific datasets.
The slope (Δy / Δx) is the rate of change between the two known points. It tells you how much y changes for every one-unit increase in x. Multiplying the slope by the distance (x − x₀) gives you the y offset from y₀.