Read the result
The percentage error is a local estimate based on differentials, so it is most reliable for small errors.
Limits and errors
Error Propagation Calculator
Estimate how measurement uncertainty affects a calculated quantity.
Formula
delta f approx f'(x)delta x; for Q=Cx^a y^b, delta Q/Q approx a delta x/x + b delta y/y
Result
Worked substitution
Error propagation is a local estimate. It works best for small measurement uncertainty.
Where it helps
Use it for engineering measurements where input uncertainty matters as much as the nominal value.
Common slip
Signed error and worst-case absolute error answer different questions.
Try it
For Q = x^n, double n and notice how the relative error scales.