Formula and example
How it is calculated
y = y₁ + (x−x₁)·(y₂−y₁)/(x₂−x₁).
Worked example
Between (10;20) and (30;60), x = 15 gives y = 30. The slope is 2.
Things to check
- The two known x values must be different.
- The calculation assumes a straight line across the range. Measurement uncertainty and curvature are not included.
Frequently asked questions
Can I enter a value outside the two points?
Yes. It is marked as extrapolation because extending the line beyond the known values requires an additional assumption.