Metal micro-nano grating has received much attention due to its ability to provide high-efficiency light absorption. However, the current research scales of these metal gratings are focused on subwavelengths, and little attention has been paid to the absorption properties of metal gratings at other scales. We investigate the absorption properties of metal gratings based on surface plasmon resonance (SPR) across the scales from superwavelength to subwavelength. Under grazing incidence, we observe continuous strong absorption phenomena from superwavelength to subwavelength Al triangle-groove gratings (TGGs). Perfect absorption is realized at the subwavelength scale, whereas the maximum absorption at all other scales exceeds 74%. The electric field distribution gives the mechanism of the strong absorption phenomenon attributed to SPR on the surface of Al TGGs at different scales. In particular, subwavelength Al TGGs have perfectly symmetric absorption properties for different blaze angles, and the symmetry is gradually broken as the grating period’s scale increases. Furthermore, taking Al gratings with varying groove shapes for example, we extend the equivalence rule of grating grooves to subwavelength from near-wavelength and explain the symmetric absorption properties in Al TGGs. We unify the research of metal grating absorbers outside the subwavelength scale to a certain extent, and these findings also open new perspectives for the design of metal gratings in the future.