Stair Calculator

Use this UK stair calculator to estimate the number of risers and treads, individual rise and going, total horizontal run, pitch angle, stringer length and an optional floor-opening or headroom value. Select the private-stair guidance profile for England, Wales, Scotland or Northern Ireland, enter your finished dimensions, and review each dimensional check.
This is a planning and dimensional screening tool, not Building Control approval. Stair rules depend on the jurisdiction, building type, use and full design. Confirm the current requirements for your project before construction.

How do I calculate stairs in the UK?

Measure the finished floor-to-floor rise, choose a whole number of risers, and calculate the individual rise. Enter the individual going or total horizontal run to calculate the number of treads, overall run, pitch and stringer length. Then compare the result with the private-stair guidance for England, Wales, Scotland or Northern Ireland.

What is the 2R + G stair formula?

2R + G means twice the individual rise plus the going. For example, a 190mm rise and 250mm going gives (2 × 190) + 250 = 630mm. The reviewed private-stair guidance profiles use a 2R + G range of 550–700mm.

How many stair risers and treads do I need?

For an equal-riser layout, divide the finished total rise by a practical target rise, round to a whole riser count, then divide the total rise by that count. For example, 2,600mm divided by 14 gives 185.7mm per riser. A standard straight flight normally has one fewer tread than risers, so 14 risers usually means 13 treads.

What is the maximum pitch for a private stair?

The reviewed private-stair guidance profiles use a maximum pitch of 42 degrees. A stair can still fall outside guidance below 42 degrees if its rise, going or 2R + G value is outside the selected limits. Do not automatically combine the maximum rise with the minimum going.

How much stair headroom is normally required?

Normal clear headroom is 2,000mm, measured vertically above the pitch line of the flight and over the landing. Limited alternatives can apply to some loft or roof-space conversions. Check the current guidance for the relevant UK nation and confirm the proposal with Building Control.

Does a passing result prove Building Regulations compliance?

No. A pass means the dimensions checked by the calculator are within the selected private-stair guidance profile. It is not Building Regulations approval and does not assess the complete stair, structure, landings, handrails, guarding, fire safety, access requirements or project-specific conditions.

Stair calculator terms explained

Total rise is the finished floor-to-floor height. Individual rise is the vertical height between consecutive tread levels. Going is the horizontal nosing-to-nosing distance. Total run is the horizontal length of the flight. Pitch is the stair angle. Stringer length is the calculated sloping length of the supporting member.

Can I use this calculator for winder or turning stairs?

No. This calculator models a straight flight only. Winder, tapered, quarter-turn, half-turn and spiral stairs require additional geometry, prescribed measurement positions, landing checks and project-specific design. Use this result only for the straight portion unless a separate tool explicitly supports the full configuration.

How to use the UK stair calculator

Select units and guidance profile. Metric is recommended for UK regulatory checks. Choose the nation in which the work will be carried out.
Choose the mount and run mode. Standard mount normally treats the upper floor as the final level; flush mount adds a tread at the upper level. Enter either an individual going or the total horizontal run.
Enter the total rise. Measure vertically from the finished lower-floor level to the finished upper-floor level. Include the thickness of finishes that will be present when the stair is used.
Add optional constraints. Fixed Rise preserves the entered regular riser height; Fixed Number of Steps uses the entered count. Use only one constraint at a time and clear the unused optional value before recalculating. Tread thickness, nosing and headroom inputs are optional.
Calculate and review every check. A pass means the entered or calculated value is inside the selected dimensional range. It does not confirm the whole stair is compliant.

Illustration of different parts of standard staircase

UK private stair rise, going and pitch limits

The calculator uses separate guidance profiles because stair guidance is not identical throughout the United Kingdom. The table below summarises the private-stair dimensions checked by this tool.

UK private stair rules at a glance

Private-stair limits are not identical across the UK. England uses a 150–220mm rise and 220–300mm going. Wales states a maximum 220mm rise and minimum 220mm going, with permitted rise-and-going combinations in Approved Document K. Scotland uses a 100–220mm rise and minimum 225mm going. Northern Ireland uses a 75–220mm rise and minimum 220mm going. All four reviewed profiles use 2R + G of 550–700mm, a maximum pitch of 42 degrees and normal headroom of 2,000mm.

Profile	Rise checked	Going checked	2R + G	Maximum pitch	Normal headroom
England	150–220mm	220–300mm	550–700mm	42°	2,000mm
Wales	Maximum 220mm; permitted combinations apply	Maximum 220mm; permitted combinations apply	550–700mm	42°	2,000mm
Scotland 2026	100–220mm	Minimum 225mm	550–700mm	42°	2,000mm
Northern Ireland	75–220mm	Minimum 220mm	550–700mm	42°	2,000mm

These are selected dimensional checks for private stairs. Other stairs can have different limits. The complete guidance also covers landings, tapered treads, guarding, handrails, open risers, doors, access, fire safety and other matters that this calculator does not assess.

Setting the Foundation: Choosing Your Units and Layout

Right then, let’s get the foundation laid before we start pouring the concrete. When you first sit down to design a staircase, you’re immediately faced with two big choices: units of measurement and layout. Look at the calculator just above, see those toggles? They’re there for a reason. Don’t waste time trying to convert five feet, nine and a quarter inches into millimeters on a scrap of paper or pocket calculator, that’s just inviting errors. Choose your unit, be it Metric (m/mm) or Imperial (ft. /inch), and stick with it from the jump.

Standard Mount

The last step is one step below the upper floor level, the upper floor itself is treated as the last step.

Your total number of risers one more than total number of steps.
Often easier to frame on decks.
Helpful when space is tight.

Illustration of General Mount Type Stairs Style

Flush Mount

The top step is at the same height as the upper floor/ deck landing.

Total number of risers and steps are same.
Gives a clean, continuous line of steps right up to floor level.
The transition feels smoother.
It requires high skills to frame.

Illustration of Flush Mount Type Stairs Style

Stairs Terminologies

When you use this stairs calculator, there are four main measurements you really need to understand. If you get these right, most of the stair design becomes much easier.

Total Rise

Total rise is the vertical distance from the finished floor below to the finished floor above. Not the concrete or structure, but the final surface you will walk on. On site I always measure this in a few different spots, because floors are rarely perfectly level. If you only measure once and it is slightly off, you can end up with small differences in step heights later, and that usually causes problems.

Total rise = number of risers × rise per step

Total Run

Total run is the horizontal length that the staircase will cover. Think of it as how far the stair comes out along the floor, not counting any landings or extra openings. This is the key number when you plan the opening in a floor or check if the stair will fit in a small space like a corridor. If the total run is too short, the stairs become steep and uncomfortable.

Total run = one run × number of steps

Riser (Rise Height)

One step rise is simply how high your foot lifts from one step up to the next. It sounds an easy thing, but this is the point where things start to get very wrong. Every single rise should be the same, from the very first step at the bottom to the last one at the top.

Important!

According to IBC:
Riser between: 4 in and 7 in ( 102–178 mm)

Important!

According to IRC:
Max riser height: 7¾ in (197 mm),
Min riser height: 4 in (102 mm)

Step Run (Run/ Tread Depth)

Step run is the depth of your stair step, the part your foot actually stands on. If this depth is too small, you do not feel secure when you go down the stairs, especially when you are carrying tools, boxes or materials. Building codes usually give a minimum tread depth for safety, and from experience I suggest you stay at or above that value. A good tread depth makes the staircase feel natural and easy to use.

Important!

According to IBC:
Tread depth: at least 11 in (≈ 279 mm)

Important!

According to IRC:
Min tread depth: 10 in ≈ 254 mm

Stair Nosing

When the tread is installed, it usually extends a little past the riser (the vertical part). That extra bit sticking out at the front is what we call the stair nose. This overhang is another subtle but important safety feature. This small overhang increases the effective run depth for your foot without making the overall staircase longer.

Head Room

Headroom is the clear vertical space above the stairs, from the stair tread up to the standard ceiling height or any structure above. It’s the space that lets people walk without hitting their head.

Stair Stringer Calculator

The stringer is the long sloping piece that the whole stair rests on (flight of stairs). It runs from one floor to the other and carries every tread and riser, so if the stringer is wrong, the stair just feels wrong too. In the calculator we mostly care about its height, length and angle. Height is the total rise R, the floor-to-floor distance. The total run T is how far the stair goes out horizontally. From those two the tool finds stringer length with Pythagoras theorem

Stringer length = √(Total rise² (R) + Total run² (T))

Stringer height= Total rise (in case of flush Mount)
Stringer height= Total rise – Step Rise (in case of Standard Mount)
Stair stringer angle comes from
θ = arc tan(R / T)
Angle = arctan (Total rise / total run)

Important!

Safe stringer angle is usually, around 30°–37° from horizontal plane.

The 2r + t Rule for Stair Design

The “2:1 Rule” (or 2r + t rule) is an empirical formula used to ensure that a stair feels comfortable, safe, and easy to ascend and descend. It relates the rise (r) of a step (the vertical distance) to the tread (t) of a step (the horizontal depth). The rule is expressed as

2r + t = 25 inches (or 63 cm)

Where:
r = Rise (Riser height), t = Tread (step depth), 25 inches = a constant value within a comfortable range.

What is the 27 rule for stairs?

The rule is based on the biomechanics of walking and climbing. A person naturally uses twice as much energy to lift their body vertically (the rise) as they do to move it horizontally (the tread). The formula essentially aims to keep the total “effort” (or stride length) per step constant.

If 2r + t is too small

The stair feels stumbling or too steep. The steps are cramped, making your stride short and forcing you to lift your knee high.

If 2r + t is within the ideal range

The stair feels natural and comfortable. Your body’s natural stride rhythm is maintained whether climbing up or down.

If 2r + t is too large

The stair feels awkward or stretching. The steps are too long and shallow, forcing a long, unnatural stride that can lead to missteps.

Example: If a comfortable stair has a Rise (r) of 7 inches and a Tread (t) of 11 inches:

2(7) + 11 = 14 + 11 = 25 inches

Since 25 inches falls within the comfortable range, this stair would generally feel very natural and easy to use.

Whole Steps, No Weird Fractions

Another key job is finding a clean whole number of steps. The tool works out how many steps you need so the total rise is split evenly, no odd half step at the top or bottom like. Those steps are where people catch their toe. Sticking to whole numbers reduces trip risk and also saves you from wasting material trying to “fix” things later.

How to Use Stair Calculator

Steps	What to Do?	Details
Step-1	Select your units	Choose whether you want to work in feet & inches (or meter/mm) at the top of the calculator.
Step-2	Pick the mount type	Choose Standard or Flush mount, depending on how your stringer stair will attach to the top floor
Step-3	Choose the run input mode.	One Run: enter your chosen run depth of a single run. Total Run: use this if you know the full horizontal length available of the staircase.
Step-4	Enter the total rise and run.	Type your Total Rise (floor-to-floor height). Enter your Single or Total run, depending on your “run input mode” (Note: you can hit enter at this point and calculator will give you your optimum stair calculation or move to more customized input values)
Step-5	Set optional rise / step controls.	Under “Optional Input Values”, choose one of these if you want more control: Fixed Number of Steps: enter how many steps you want the staircase to have. Fixed Rise (Step Height): enter the exact step height you want.
Step-6	Configure tread options (optional)	Turn Tread ON if you want to include tread thickness in the calculation, then enter the tread thickness in inches/mm.
Step-7	Set nosing options (optional).	Turn Nosing ON if your steps will have a nosing. Enter the nosing projection (how far the nosing sticks out).
Step-8	Use the headroom constraint (optional).	Turn Headroom Constraint ON if you need to check clear headroom. Then choose: Floor thickness & Required Headroom, or Floor thickness & Floor Opening Length, and fill in the requested values.
Step-9	Click “Calculate”	Press the Calculate button. The tool will generate stair layouts based on your inputs.

If you want to design concrete stairs and want to know the materials for it,

Click Here

Use these values to check comfort (riser height and tread depth), space (total run and angle), and what materials you need (stringer length, number of stair treads, tread thickness).

Advanced Safety Features

Consistent Rise

All steps should have uniform riser height. Even small changes in rise can feel like a “Missing step” and increase the risk of trips and falls.

Proper Headroom

Stairs need clear headroom from the tread to ceiling, so people don’t have to duck or in worst case smash their head. In most cases, aim for at least 80 inches (about 2.0 m) of vertical clearance.

Handrails

Stair rail on one or both sides give you something solid to grab, and that really matters for kids, older folks, or just anyone who’s a bit tired and clumsy after a long day. You don’t really notice them when things are fine, but you’re glad they’re there when you miss a step.

Lighting

is a big one too. If the landings and the front edge of each step are well lit, it’s much easier to see where one tread ends and the next one starts. No guessing, no “is that the last step?” moment in the dark.

Non-Slip Surface

Give your stairs a surface that grips. Use non-slip treads and keep the surface dry. A bit of texture, engraving, grip tape, or a stair runner can prevent slips.

Frequently Ask Questions (FAQ’s)?

People often ask “how many stairs in a flight” and my simple answer is “there isn’t one fixed number “The exact number depends on:

The total rise (floor-to-floor height).
The single step height allowed by your local building code or chosen by you.

A flight of stairs is one continuous run of steps with no break or landing in between. For example, 14 steps going straight up from one floor to the next is one flight. If there’s a landing in the middle, you now have two flights of stairs (one below the landing, one above).

For most homes, stairs are usually about 36 inches (around 915 mm) wide. This is a common minimum stair width that feels okay for one person. Wider stairs (like 40–48 inches) are more comfortable, especially for deck stairs or busy areas. Always check your local building code, then use our stair calculator to plan your stair size.

The easy way: just enter your total rise, and either your step height or tread depth, into our stair calculator and it will automatically work out the number of steps, step rise, step run, and stair stringer length for you.

If you’re wondering how to measure stair stringers, we mention it in detail above in the content, and if you don’t want to do the math, just enter your measurements into our stair calculator and it works out everything for you like angle, length and height of stringer.

Cut the top of the stringer so it sits flat against the landing.
Fix it to the landing frame with metal brackets and strong screws/bolts.
Make sure the top step is the same height as all the other steps.

To build deck stairs, first measure the total rise from the ground to the top of the deck. find the number of steps, step rise, tread depth, and stair stringer length. Cut your stair stringers, attach them securely to the deck frame, follow building code for deck stairs for comfortable build.

For stairs:

Measure the total rise (floor to floor height).
Measure the total run (horizontal distance of the stairs).
Solve: rise ÷ run → this is your rise over run (slope).

There isn’t one perfect rise and run for stairs, but there is a very common “comfort zone.”
For most houses, a good stair size is around 7–7½ inches rise and 10–11 inches run (about 175–190 mm rise and 250–280 mm run). That keeps your stair rise and run comfortable and close to the 27 rule for stairs. You can try different sizes in our stair calculator to see what works best for your space and local code.

For most modern homes, an 8 inch step is usually too high. Many building codes aim for a stair rise around 7–7½ inches. Higher steps feel harder to climb, less safe for kids and older people, and may not meet stair code in your area.