Fulbourn windmill is a smock mill, 42 feet high and with three working floors. The octagonal round house is of brick; above it is the oak framed smock with oak cant posts and binders and weather-boarded.
On the smock rests a revolving cap carrying the sails and fantail. The cone-shaped cap, sheathed in copper, is fitted with a wooden skirt.
The sails are doubled shuttered clockwise patent sails. The shutters open and close according to the strength of the wind through the spider on the hub of the sails. The fan at the rear turns the cap via gears so the sails faced the wind.
The sails turn the 10 foot diameter brakewheel in the cap which transmits the power downwards to the vertical shaft via the wallower. The 9 foot diameter spur wheel at the base of the vertical shaft connects to the stones, turning the top stones. The uppermost floor has three grain bins feeding the three pairs of stones on the middle floor with chutes down to the ground floor. When the stones are revolving the action of the grooves are like scissors opening and shutting 90-120 times a minute. (One revolution of the sails will turn the stones 15 times)
On the northwest face wall of the roundhouse is an external wheel for transmitting power from a standing engine to the third pair of stones.
The mill consists of a wooden tower, the smock, on a brick base surmounted by a cap and sails which can be turned to face the wind.