Stair Angle Calculator
Check how steep a staircase is. Enter the height of one step (riser) and its depth (going or tread), or the total rise and total run, and get the stair angle in degrees with a plain-English rating from gentle to too steep.
Calculate stair angle
Stair angle formula
Angle
Angle = arctan(riser ÷ going)Use one step or the whole flight; the ratio is the same. A 180 mm riser with a 250 mm going gives arctan(0.72) = 35.8°.
Stair angle guide
| Angle | What it means |
|---|---|
| Under 20° | Very shallow; consider a ramp (ramps are usually under about 5–7°) |
| 20°–30° | Gentle; common in public buildings and external steps |
| 30°–37° | Ideal range for homes; comfortable to climb and descend |
| 37°–42° | Steep but within UK limits for private stairs |
| 42°–50° | Too steep for a normal stair; loft-access or space-saver territory |
| Over 50° | Ladder or ship’s ladder |
Common riser and going combinations
| Riser | Going | Angle | 2R + G |
|---|---|---|---|
| 150 mm | 300 mm | 26.6° | 600 mm |
| 170 mm | 280 mm | 31.3° | 620 mm |
| 180 mm | 250 mm | 35.8° | 610 mm |
| 7 in | 11 in | 32.5° | 25 in |
| 7¾ in | 10 in | 37.8° | 25.5 in |
| 220 mm | 220 mm | 45.0° | 660 mm |
Frequently asked questions
What is a good angle for stairs?
Between 30° and 37° feels natural for most people. UK regulations allow up to 42° for private stairs.
Is a 45 degree staircase too steep?
Yes for a main staircase. 45° is beyond the 42° UK limit and only suits loft or space-saving stairs.
How do I measure the angle of existing stairs?
Measure one riser and one going and use this calculator, or lay a straight board across the nosings and read it with a digital angle finder.
Related calculators
Ratings are general guidance. Follow your local building regulations for stair design.