Staircase Rise, Run & Railing Calculator

Staircase Design Guide

What's the key thing to understand about UK Building Regulations Part K?

Approved Document K sets stair dimensions. Private stairs (domestic): rise maximum 220mm. Going minimum 220mm. Pitch maximum 42°. The '2R + G = 550-700mm' formula: twice the rise plus the going should be 550-700mm (ergonomic comfort zone). Loft conversion stairs: allowed up to 42° pitch and 220mm rise, but going can be as low as 145mm for alternating tread stairs. Public/commercial: rise maximum 180mm. Going minimum 280mm. Open risers: if open, the gap must prevent a 100mm sphere passing through, to prevent young children getting stuck or falling.

What should I know about Calculating Stair Dimensions?

Number of risers = floor height / target rise. Round to nearest whole number. Actual rise = floor height / number of risers. Example: 2600mm floor height. Target rise 175mm. 2600/175 = 14.86 → round to 15 risers. Actual rise = 2600/15 = 173.3mm. Using 2R+G formula: G = 600 − 2×173.3 = 253mm going. Total run = going × (number of risers − 1) = 253 × 14 = 3,542mm horizontal floor space. Note: number of treads = number of risers − 1 (the top landing counts as a tread, not a separate step).

What's the key thing to understand about Handrails and Balustrading?

Handrail height (domestic): 900mm minimum from pitch line (surface of tread nosings) to top of handrail. Baluster spacing: maximum 100mm gap — a 100mm diameter sphere must not be able to pass through (child safety). Handrail required: on any staircase with a total rise exceeding 600mm. Both sides: on stairs wider than 1000mm. Newel post positioning: at the start, end, and any change of direction. Timber stair regulations: notching structural timber for staircases is strictly limited — consult a structural engineer or building control before cutting into any load-bearing stair stringer, since removing too much material can seriously weaken it.

What's the key thing to understand about Common Staircase Mistakes?

Inconsistent rises: if any single step is different from the others, it is a significant trip hazard. All rises must be the same within 5mm tolerance. Wrong starting point: the measurement of floor-to-floor height must be exact — measure between finished floor levels, not subfloor. Ignoring headroom: calculate headroom from the pitch line, not just the height at the bottom. Low ceilings eat headroom rapidly as the stairs ascend toward a landing. Undersize going: a short going feels steep and unsafe underfoot, even if the rise-to-going ratio technically passes the minimum regulatory requirement.

What should I know about the Pitch Line and Headroom Requirements?

Part K specifies a minimum headroom of 2000mm measured vertically from the pitch line (an imaginary line connecting the front edge/nosing of each tread) to any ceiling, beam, or structure above, reducing to 1900mm in loft conversions where full headroom genuinely can't be achieved due to roof pitch constraints. This headroom requirement is frequently the limiting factor in tight loft stair designs — it's not just about the stairs' own rise and going, but the available vertical space all along the stair's full length, including at the point where the stair passes beneath the floor opening above it. Measuring headroom at several points along the stair run (not just the bottom or top) is essential before finalising a design, since roof slopes mean the critical pinch point is often somewhere in the middle of the flight, not at either end.

What do I need to know about Going Measurement Methods?

'Going' is measured differently depending on whether a staircase has open risers (gaps between treads, no vertical riser board) or closed risers. For closed-riser stairs, going is measured as the horizontal distance between the front edges (nosings) of consecutive treads. For open-riser stairs, Part K requires going to be measured including an assumed 16mm nosing overlap even if treads don't physically overlap, to keep the calculation consistent and prevent a technically-compliant but practically cramped design. A common error in DIY staircase planning is measuring going as the full tread depth rather than the nosing-to-nosing distance — these differ whenever treads have a projecting nosing (commonly 16-25mm), meaning a tread that's 250mm deep might only contribute 225-234mm of actual 'going' toward the 2R+G calculation.

What should I know about Loft Conversion Staircase Space-Saver Rules?

Loft conversions are the one place in UK domestic regulations where a non-standard staircase is explicitly permitted, because the available floor space is so often too tight for a compliant straight flight. Approved Document K allows 'space-saver' or 'alternating tread' staircases for loft conversions specifically, where there is genuinely no room for a conventional stair — these have paddle-shaped treads with alternating cut-outs that let your foot go further forward, allowing a steeper pitch (up to roughly 56° compared with the normal maximum around 42°) and a shorter run. Space-saver stairs must still meet minimum going and rise rules under the alternating-tread provisions, and they can only be used for access to a single habitable room (plus a bathroom), not as the only stair serving multiple rooms. They're also only acceptable where it can be shown that a standard staircase physically will not fit — Building Control will usually want to see that you've tried to maximise the conventional option first. Handrails are still required, and headroom rules still apply, just measured along the steeper pitch line.

Reference: Compliant Rise/Run Combinations Under Part K

The "2 x rise + going" rule of thumb is a long-standing proxy for a comfortable, safe stride pattern on stairs; most UK Building Regulations Part K-compliant private stairs land somewhere in the 190-220mm rise and 220-280mm going range, with a maximum rise of 220mm and a minimum going of 220mm being the hard regulatory limits for a private stair, not just guidance.

Worked Example: Calculating Steps for a Given Floor-to-Floor Height

A loft conversion has a floor-to-floor height of 2,700mm. Targeting a comfortable rise of around 200mm (within the regulatory maximum of 220mm): Number of risers = 2,700 / 200 = 13.5, rounded up to 14 risers (always round up, then recalculate the actual rise) Actual rise = 2,700 / 14 = approximately 193mm, a comfortable, fully compliant figure With 14 risers there are 13 goings (one fewer going than risers, since the top step is the landing/floor itself). Applying the 2R+G guide rule to find a matching going: 2 x 193 + G = roughly 630, so G = 244mm, comfortably within the compliant range. Total horizontal run (the "going length" the staircase will occupy in plan) = 13 goings x 244mm = approximately 3,172mm, just over 3.1m of floor space needed for a straight flight — a figure worth checking against the available landing-to-landing distance early in a loft conversion design, since a straight stair that does not fit often forces a switch to a space-saving winder or alternating-tread design, each with its own separate Part K rules covered elsewhere on this page.

What's the key thing to understand about Choosing a Staircase Layout?

Before rise and run numbers matter, the layout decision drives most of the space and cost outcome. A straight flight is the cheapest to build and easiest to get compliant, but needs the most uninterrupted floor length. An L-shaped (quarter-turn) staircase with a half-landing uses less linear space and can turn a staircase to fit an awkward room, at the cost of one or two extra newel posts and more complex stringer cutting. A U-shaped (half-turn) staircase packs the most rise into the smallest footprint but needs a landing wide enough to meet going requirements through the turn, and winders (tapered treads replacing a square landing) can achieve a similar space saving with a smaller landing but concentrate tripping risk on the narrow end of each winder tread. Choosing layout first, then checking rise/run compliance within that chosen footprint, avoids the common mistake of calculating a perfect straight-flight rise and run only to discover the room isn't long enough to fit it.

What do I need to know about Stringers, Treads and Construction Method?

Once rise and going are set, a carpenter cuts the stringers — the sloped side boards that carry the treads — using the calculated rise and going to mark out each step with a saw template or framing square. A cut (open) stringer has notches cut into its top edge so each tread sits directly on the cut profile, giving a traditional exposed-step look from the side. A closed (housed) stringer stays a solid board with housings routed into its inner face so treads slot in from the side, giving a cleaner finish often used against a wall. Timber choice matters structurally as well as visually: softwood (pine) stringers are common and economical for a straight domestic flight, while hardwood is usually reserved for treads and the top nosing, where wear resistance matters most. For a flight over about 2.8m rise, UK Building Regulations Part K generally requires an intermediate landing, which also changes the stringer cutting from one long run into two shorter flights.

Reference: Typical Build Costs by Staircase Type

Swapping softwood for an oak or hardwood staircase typically adds 60-120% to the material cost, concentrated in the treads, handrail and newel posts, since the hidden structural stringers are rarely worth upgrading from softwood.