AbstractThe Schmidt hammer (SH) is widely used in geomorphology for relative‐ and calibrated‐exposure age dating surfaces and deposits within landforms. This study employs a laboratory‐based methodology to assess the effects of surface roughness, clast roundness, and clast volume on SH rebound values (R‐values) by analyzing samples from three modern depositional environments (i.e. river, alluvial fan, talus). Each environment contains clasts of Torlesse supergroup greywacke sandstones with distinct roundness and micro‐scale roughness characteristics. Roundness, surface roughness, and clast volume were all found to influence R‐values significantly. The R‐values from different deposit types are statistically significant and could potentially create an apparent age divergence of several thousand years for samples with the same exposure‐age. © 2020 John Wiley & Sons, Ltd.