PMR spacing is measured by writing a pattern on a magnetic storage layer in non-return-to-zero notation, reading the pattern from the magnetic storage layer, analyzing a first harmonic component of the pattern that has a first amplitude, analyzing a second harmonic component of the pattern that has a second amplitude, measuring a ratio between the first and the second amplitudes of the first and second harmonic components, and determining a first spacing based on the ratio. In another embodiment, spacing is measured by analyzing a third harmonic component on the magnetic storage layer that has a third amplitude, measuring a difference in the amplitudes of the second and the third harmonic components while varying the first spacing and taking the ratio of the difference of the two each harmonic components.