A washing machine appliance and method of operation for determining load size are provided herein. The washing machine appliance may include a cabinet, a tub, a wash basket, a measurement device, a motor, and a controller. The cabinet may include a front panel. The front panel may define an opening. The tub may be positioned within the cabinet. The wash basket may be rotatably mounted within the tub. The wash basket may define a wash chamber to receive an article load of one or more articles. The measurement device may detect movement of the tub. The motor may be in mechanical communication with the wash basket to selectively rotate the wash basket within the tub. The controller may be in operative communication with the measurement device and the motor.