• Forage density has a linear relation to pasture height. • The regression of forage density to pasture height is a measure of plant morphology within the sward. • Forage mass is the product of forage density and pasture height resulting in a second-order relation with zero intercept. • The form of the second-order relation of forage mass to pasture height can be diminishing return, linear, or exponential, depending on the distribution of forage density within the pasture. P late meters are used to estimate pasture forage mass (FM; lb dry matter/acre) by measuring meter-compressed forage height (CHt; inches) and multiplying that value by a forage density (FD; lb dry matter/acre/inch) coefficient. Since FD has a linear relation to CHt (Eq. 1) and FM equals FD times CHt (Eq. 2 and 3) the FM calibration model is second order with no intercept (Eq. 4). FD = a + b CHt [1] FM = FD CHt [2] FM = (a + b CHt) CHt [3] FM = a CHt + b CHt 2 [4] To test this hypothesis, 20 rotationally stocked pastures at five sites in the Alleghany Plateau (three) and Appalachian Ridge and Valley (two) of West Virginia were used to calibrate a plate meter. Sites differed in species composition: Grant, tall fescue (Schedonorus arundinaceus; previously known as Festuca arundinacea); Terra Alta, orchardgrass (Dactylis glomerata) and white clover (Trifolium repens); WVU1 and WVU2, orchardgrass, tall fescue, Kentucky bluegrass (Poa pratensis), timothy (Phleum pratense), and white clover; Pendleton, smooth bromegrass (Bromus inermis). Pastures were sampled over 3 years pre-grazing (93), post-grazing (96), and in mid-regrowth (11) for a total of 200 sampling events across the grazing season (2 May-2 December). Pastures were walked in a zigzag manner with paired CHt and FM samples taken at regular intervals, ensuring that 15 samples were taken uniformly across the pasture. A falling plate meter (Rayburn and Rayburn, 1998) was used to measure CHt. This meter is an 18-inch square, 0.22-inch thick piece of acrylic plastic , weighing 2 lb 15 oz. Pasture CHt was measured by placing the plate on the pasture and reading its height above the ground once the canopy supported its weight. Within the area measured for CHt, a 1-sq ft area was clipped at ground level. Clipped samples were oven dried at 131°F for 48 h, weighed and FM calculated. The 15 CHt and FM samples were used to calculate FD present on the day of sampling by linear regression with zero intercept