Abstract: The invention relates to an adjustable stair forming apparatus, adapted to form a flight of stairs of a settable material. The flight of stairs including a series of treads interconnected by intermediate risers. The apparatus comprises, a frame to support a series of forming units provide a forming surface. Each forming unit, includes a tread defining formwork that includes a rectangular shaped tread forming surface, slidably and pivotally mounted to the frame from or toward a first major edge of the tread forming surface. The forming unit also has a riser defining formwork that includes a rectangular shaped riser forming surface with a first major edge adjustably mounted from or toward the opposite major edge of the tread forming surface. The riser forming surface at least in part co-extending with the tread forming surface in a stair width direction.