The effect of pre-grazing herbage mass (HM) on herbage intake and milk production of strip-grazing dairy cows is usually studied at the same herbage allowance (HA). In the literature, the effect of HM seems to be affected by the cutting height above which HA is estimated. The aim of this 2 × 3 factorial study was to determine whether the effect of HM (low vs high HM) on herbage intake, milk production and grazing behaviour of dairy cows is affected by the HA estimation height (ground level vs 2·5 vs 5 cm). Two HMs were compared in three different ways: at same HA above ground level (SHA0), at same HA above 2·5 cm (SHA2) and at same HA above 5 cm (SHA5). During two consecutive years, twenty-four Holstein-Friesian dairy cows in mid-lactation were assigned to one estimation height in an incomplete switchback design, with two 14-d periods. There was an interaction between HM and estimation height for herbage intake and milk production. The effect of HM on herbage intake was positive, null and negative when HMs were compared at SHA0, SHA2 and SHA5, respectively. This study may have practical implications on future research for studying, directly or indirectly, the effect of pre-grazing HM under strip- or rotational-grazing management, and on modelling herbage intake at grazing.