Measure the floor-to-floor. Divide it by a riser height you can live with. Round to a whole number, because you cannot have half a step. That single division decides your going, your pitch, the length of your stairwell opening and whether the person walking up it brains themselves on the trimmer — and no amount of careful linework afterwards rescues a stair that was never resolved as an object.
That's the whole method. Numbers first, drawing second. What follows is how to run those numbers and then how to communicate them so the technician picks the drawing up and builds what you meant.
One caveat before the figures: everything numeric below is from Approved Document K, the England guidance, and I'd still open the current edition before you commit anything to a drawing. Scotland has its own Technical Handbooks, Ireland its own Part K, and the documents don't agree with each other.
The number you divide is the vertical distance from finished floor level to finished floor level. Finished. Not structural slab to structural slab, not screed top to joist top, not whatever the architect's section happened to say in week three before anyone picked a floor finish.
This is where a surprising number of stairs go wrong before a line is drawn. Say your ground floor is a 150mm slab with 70mm of insulation, 65mm screed and 15mm of engineered oak, and the first floor is joists with 22mm board and carpet. If you set out to the slab you'll be out by the thickness of the buildup, and the error doesn't spread itself politely across fourteen risers — it lands on the top or bottom step, which is exactly where people fall.
So: get the finishes decided, or make an allowance and flag it. Then divide.
A worked version. Floor-to-floor of 2,800mm. Try 14 risers: 2,800 ÷ 14 = 200mm exactly. Lovely. Try 2,750mm: 14 risers gives 196.4mm, which is fine — risers don't have to be round numbers, they have to be equal. That's the rule that matters. Approved Document K requires every riser in a flight to be the same height, and a 3mm variation at the top step is a trip hazard a building control officer will spot by walking it.
Note also that fourteen risers gives you thirteen goings between them, because the top riser lands you on the floor above. Count this wrong and your stair is one tread too long, which eats the landing and the headroom in one go.
Going, Pitch and the Thing Everyone Measures Wrong
Going is not tread depth. Going is measured nosing to nosing — from the front edge of one tread to the front edge of the next, in plan. The tread itself is usually deeper than the going because the nosing overhangs the riser below. A 250mm going with a 25mm nosing overlap gives you a 275mm tread. If you dimension the tread and call it the going, every geometry check downstream is wrong.
Approved Document K sets, for a private stair in a dwelling, a maximum rise of 220mm, a minimum going of 220mm, and a maximum pitch of 42 degrees. It also gives the relationship rule: twice the rise plus the going should fall between 550mm and 700mm.
Run our 200mm riser through it. 2R + G = 700 means a going of 300mm; 2R + G = 550 means a going of 150mm, which fails the 220mm minimum. So the comfortable window for a 200mm rise is roughly 220mm to 300mm of going. Pick 250mm and you get a pitch of arctan(200/250), about 38.7 degrees. Within limits, and it won't feel like a ladder.
Multiply going by the number of goings and you have the plan length of the flight: 13 × 250 = 3,250mm. Now you know whether the stair actually fits the hole you drew for it. In practice this is the moment half of student stairs die — the flight is 3,250mm long and the void in the plan is 2,400mm, and rather than fix the plan the stair quietly gets squashed.
Headroom Is Measured From the Pitch Line, and That's Why Yours Fails
Draw a line through the nosings of every tread. That's the pitch line, and it is the datum for almost everything: headroom, handrail height, the angle you dimension.
Approved Document K asks for 2,000mm of clear headroom over the full width of the stair, measured vertically from the pitch line to the underside of whatever is above — trimmer, ceiling, bulkhead, the corner of a duct nobody told you about. Vertically. Not perpendicular to the pitch. That distinction trips people up in both directions: some measure perpendicular and think they've got clearance they haven't, others assume the tight spot is halfway up the flight when it is almost always at the top, right where the stairwell opening is trimmed.
There's one relaxation worth knowing: for loft conversions where the full 2,000mm isn't achievable, Approved Document K allows reduced headroom of 1,900mm at the centre of the stair width tapering to 1,800mm at the side. That's a loft exception, not a general excuse.
The test takes two minutes. On your section, draw the pitch line. Offset it 2,000mm vertically. Wherever that offset line crosses the floor construction above, that's the earliest point your trimmer can sit. Measure back horizontally to the bottom riser — that's the minimum stairwell opening length. If the opening you've drawn in plan is shorter, you have a headroom failure, and you had it the moment you set the riser count.
Do this before you draw a single tread.
Plan Conventions: Break Line, Arrow, and What's Above the Cut
A floor plan is a horizontal slice. In the course we cut ours somewhere in the 1,200 to 1,400mm band — high enough to catch window heads sensibly, low enough to read as a plan — and that cut plane is what the stair break line is actually representing.
So the break line isn't decoration. It sits where the flight passes through the cut plane. With a 200mm rise and a 1,300mm cut, you're through after six or seven risers, and that's where the line goes. Draw it as a single diagonal, or the conventional pair of parallel diagonals, right across the flight width. Everything below it is cut and drawn solid. Everything above it — the rest of that flight, the landing soffit, the flight coming back over the top — is drawn dashed, because you are looking up at it.
This is the part that makes a drawing unambiguous. Dashed linework above the cut is not just convention for its own sake; it is how you prove to yourself that the upper flight clears the lower one. We teach it in the stairs lesson alongside the dashed-over layer for exactly that reason — the dash tells you where the thing you can't see is sitting.
Then the rest of the plan furniture:
Direction arrow. One per flight, running along the centre of the stair, starting at the bottom riser of the flight you're standing on and pointing in the direction of travel. Label it UP or DN relative to the floor the plan represents. A ground floor plan says UP. The first floor plan of the same stair says DN.
Riser count in the label. "UP 14R" tells the technician the whole story in four characters. If they count thirteen treads on your drawing and the label says fourteen risers, they know the top one is the floor and nobody has to ring you.
Dimension string along the flight. Overall flight length, then the going as a repeated dimension — "13 @ 250 = 3,250". Never dimension each tread individually. You're asking for a typo and inviting someone to build them unequal.
Nosing lines. Each nosing drawn as a line, lighter than the cut walls. Don't let the stair out-shout the structure.
Handrail and balustrade in plan. Both sides where both exist, drawn as a thin double line, continuing round the landing. If you don't draw it in plan you will never notice that it crashes into the first floor guarding.
The Section: Prove It, Don't Just Depict It
Cut the section along the length of the flight, not across it. A section across a stair tells you nothing useful.
What has to be on it: the pitch line, nosings and treads, a dimension string of risers ("14 @ 200 = 2,800") running vertically and a string of goings running horizontally, both finished floor levels annotated as levels, the floor buildups either end so the FFL-to-FFL dimension is honest, the trimmer or beam forming the stairwell opening, and the headroom dimension drawn as an actual vertical dimension from pitch line to soffit at the tightest point. Not a note saying "2000 clear". A dimension, drawn where it's measured, so anyone can check it with a scale rule.
Handrail next. Approved Document K puts handrail height between 900mm and 1,000mm, measured from the pitch line on the flight and from floor level on a landing — and a stair 1,000mm wide or more wants a handrail on both sides. Guarding to a stair or landing in a dwelling is a minimum of 900mm, and the gaps in it mustn't let a 100mm sphere through. Draw the balustrade properly in section, with the infill, and the nasty junction at the top where the raking handrail meets the level guarding on the floor above will reveal itself immediately.
The Three Things a Reviewer Catches First
Headroom at the landing. Not mid-flight. The top three or four risers under the trimmer, and the half-landing where a bulkhead or the underside of the return flight closes in. Check both, dimension both.
Winder goings measured in the wrong place. On tapered treads the going isn't measured at the middle of the tread or at the handrail — Approved Document K measures it along the walking line, which for a stair under 1,000mm wide is the centre of the flight, and for a wider stair is 270mm in from each side. It also sets a minimum going of 50mm at the narrow end. Draw the walking line on the plan as a thin construction line and dimension the goings against it. Nine times out of ten the winders a student copies off a precedent don't achieve the going at that line, and they only fail once the line is drawn.
Handrail that stops. The handrail runs out at the top riser, doesn't continue across the landing, and nobody has resolved where it meets the first floor guarding. It's invisible in plan if you didn't draw the rail, and invisible in section if you only sectioned the flight. Draw it in both and the gap announces itself.
Then Cover Yourself
Stairs get fabricated off your drawing by someone who measured the actual opening three months after you drew it, and site is never exactly what the drawing said. So dimension the stair from a stated datum, give the FFL-to-FFL figure explicitly, and add the note that saves the argument: all risers to be equal; dimensions to be verified on site prior to fabrication.
And if a finish isn't fixed, or the structural engineer hasn't confirmed the trimmer depth, don't guess a riser height and hope. Cloud the area and mark it in abeyance with the reason — we devote a whole lesson to this habit because it's the cheapest insurance in drawing production. A clouded note that says "stair geometry subject to confirmation of first floor zone" costs you thirty seconds and is the difference between a conversation and a claim.
Get the division right, test the headroom before you draw, then let the conventions do the talking. A stair drawn that way doesn't need defending.
