Stair Stringer Calculator
Calculate exactly how many steps you need for any change in height, with riser and tread dimensions that meet building regulations. Avoid dangerous staircases from incorrect geometry.
Stair Building Regulations
UK Building Regulations
For domestic stairs: maximum riser 220mm, minimum tread 220mm. The '2R + G' rule (2 × riser + going) should equal 550–700mm for comfortable stairs. Ideal riser is 175–190mm, ideal tread 250–275mm.
The Stringer Length Formula
Stringer length = √(total rise² + total run²) using Pythagoras. Add 50–100mm for the top and bottom connections. Standard stringer timber is typically 285–300mm wide to allow for notching.
Consistent Risers Are Critical
All risers must be exactly the same height — even a 3–4mm variation is a trip hazard and building code violation. Calculate the exact riser by dividing total rise by number of steps, then verify against regulations before cutting.
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