Construction calculator UK: Part K and Type 1

UK building work is in millimetres, with England's figures in the Approved Documents. A private stair has a rise of 150 to 220 mm, a going of 220 to 300 mm and a 42° pitch at most (Approved Document K), spindle gaps must stop a 100 mm sphere, and studs and joists usually sit at 400 or 600 mm centres.

Which building rules apply in the UK?

In England, the Building Regulations set what the work must achieve and the Approved Documents give guidance on how to meet them: A for structure, H for drainage, K for stairs and guarding, M for access. Building control, from your local authority or a private building control body, decides whether your job meets them. Wales and Scotland publish their own guidance and Northern Ireland has its own rules, which can differ, so the figures on this page are England's.

Does a 2600 mm stair pass Approved Document K?

Yes, with the right going. Check four numbers against Approved Document K, Table 1.1, for a private stair: rise 150 to 220 mm, going 220 to 300 mm, twice the rise plus the going (2R + G) normally 550 to 700 mm, and a pitch of 42° at most. Headroom is 2.0 m above the pitch line (paragraph 1.11).

Worked example: 2600 mm floor to floor, finished floor to finished floor.

A comfortable stair with a 220 mm going: target riser (600 − 220) ÷ 2 = 190 mm, and 2600 ÷ 190 = 13.7, so 14 risers of 2600 ÷ 14 = 185.7 mm and 13 treads, 13 × 220 = 2860 mm of going. 2R + G = 591.4 mm, pitch arctan(185.7 ÷ 220) = 40.2°. It passes.
A tighter stair with 13 risers of 2600 ÷ 13 = 200 mm and 220 mm goings: the rise and the going are both in range, but the pitch is arctan(200 ÷ 220) = 42.3°. It fails the 42° limit.
Widen the going to 225 mm: arctan(200 ÷ 225) = 41.6°, and 2R + G = 2 × 200 + 225 = 625 mm. It passes, in 12 × 225 = 2700 mm of going.
Stairwell opening for that stair with a 250 mm floor zone (an example) and 2000 mm headroom: (250 + 2000) × 225 ÷ 200 = 2531.3 mm.

In the app: Home ▸ Stairs ▸ Rise + Run, Total Rise 2600, Total Run 2700, Desired Riser Height 200 and Floor / Joist Thickness 250 give 13 risers of 200.0 mm, 12 treads of 225.0 mm and a Stairwell Opening of 2531.3 mm. Its Incline Angle reads 43.92°, because it measures the straight line from the foot of the first riser to the top of the last. The pitch Approved Document K limits is the line through the nosings, arctan(riser ÷ going), so check that one: 41.6° here. The app doesn't do winders or landings, so a turning stair is worked flight by flight. More in stairs in a tight space and how big a stairwell opening needs to be.

Free stair calculator: set Check against to England (Approved Document K), pick Rise + run, enter 2600 and 2700 mm and set the desired riser height under Advanced to 200 to see the pitch line checked.

How far apart can stair spindles be?

Close enough that a 100 mm sphere can't pass through any opening in the guarding (Approved Document K, paragraphs 1.39 and 3.3), so every gap is under 100 mm. In a house, guarding is needed at the sides of flights and landings where the drop is more than 600 mm (paragraph 1.41), and Diagram 3.1 gives 900 mm for stairs and landings and 1100 mm for external balconies. Open risers take the same sphere test, with treads overlapping by at least 16 mm (paragraph 1.9).

Worked example: a 3000 mm run of 42 mm spindles. The fewest spindles that keep the gap under 100 mm: (3000 − 100) ÷ (42 + 100) = 20.4, so 21. Gap = (3000 − 21 × 42) ÷ 22 = 96.27 mm, or 138.27 mm on centres.

Do it in a second in MeisterCalc

Open Home ▸ Baluster Spacing and enter Run 3000 mm, Baluster Width 42 mm and Max Spacing 140 mm. The app counts from the maximum you enter, and 140 gives the same 21 as the hand sum. It shows Number of Balusters 21, Between Balusters 96.3 mm (the 96.27 rounded to one decimal) and On Centres 138.3 mm. It draws the panel with the balusters spaced across the run, labelled Run 3000.0 mm, Width 42.0 mm and Between 96.3 mm, as you type.

On Home, tap Baluster Spacing
Enter run 3000, width 42, max 140 mm
Read 21 balusters, 96.3 mm gaps
Scroll on for the rest of the table

UK jobs use Stairs, Baluster Spacing, Stud Counter, Running Measurements, Concrete, Gravel, Pitch and Check Square most. MeisterCalc has 16 calculators. Concrete, Stairs and Check Square are free; the other 13 unlock with a weekly subscription (3-day free trial) or a one-time lifetime unlock. Get MeisterCalc on Google Play

The app's count keeps every gap under the Max Spacing you enter but isn't always the fewest spindles: enter 100 and it gives 29 spindles with 59.4 mm gaps. On a stair the run is along the rake, so measure the finished openings, including next to each newel. The rule in full is in the maximum gap between stair spindles in the UK.

Are studs and joists at 400 or 600 centres?

Usually, though the Approved Documents set no figure. A plasterboard partition follows the board maker's guide, and a load-bearing wall or floor follows the structural design; Approved Document A points to the TRADA span tables for sizing floor and roof members. The reason for 400 and 600 is arithmetic: both divide a 1200 mm wide plasterboard sheet (3 or 2 spaces) and a 2400 mm floor board (6 or 4) exactly, while 450 does not. The floor deck caps the spacing too: West Fraser gives 450 mm for 18 mm CaberFloor and 600 mm for 22 mm.

Worked example: a 4200 mm partition. At 400 mm centres: 4200 ÷ 400 = 10.5, up to 11 spaces, + 1 = 12 studs. At 600 mm: 4200 ÷ 600 = 7, + 1 = 8 studs. Noggins, openings and plates come on top. Don't mix systems: 16 in is 406.4 mm, not 400. Sources in stud spacing for a UK stud wall and joist spacing in the UK.

How much fall and Type 1 does a patio need?

Approved Document H recommends a gradient of at least 1 in 60 on paving, away from the building, and no more than 1 in 40 across a path. The sub-base is area × compacted depth, then tonnes from your merchant's density.

Worked example: a 4 × 3 m patio falling 3 m away from the house.

Fall: 3000 ÷ 60 = 50 mm, so the far edge sits at least 50 mm below the edge at the house.
Type 1 at 100 mm compacted (an example depth: take yours from the paving maker or installer): 4 × 3 × 0.1 = 1.2 m³.
Tonnes: 1.2 × the merchant's compacted tonnes per m³, plus about 10 percent. Bulk bags are sold by weight or by volume, so divide by what your bag holds and round up.

This page gives no Type 1 density, because it varies by product. The app's Gravel calculator takes any density you type. Rainwater drains follow the same sum: 75 and 100 mm drains at not less than 1:100, so a 12 m run falls at least 120 mm. More in how much fall a patio needs, how much road base or Type 1 do I need and drainage pipe fall.

Free slope and fall calculator: choose Rise over a length, leave Written as on 1 in X, and enter 60 and 3000 mm for the 50 mm patio fall.

How many packs of concrete for fence posts?

Volume of the holes, plus 10 percent, divided by the yield on the pack. Ten holes 250 mm across and 600 mm deep (example sizes: use the fence maker's):

Per hole: π × 0.125² × 0.6 = 0.0295 m³; ten holes: 0.2945 m³.
With 10 percent: 0.3240 m³.
Heidelberg Materials 40N Concrete MaxiPack20 yields 0.008 m³ a pack: 0.3240 ÷ 0.008 = 40.5, so 41 packs.

Mixing your own from ballast and cement is a mix-ratio sum, and MeisterCalc has no mix-ratio mode: it gives the volume, and the ratio on the bag or from your engineer gives the cement. See concrete for post holes.

Which MeisterCalc calculators suit UK work?

The app was made metric first for the UK, Australia and New Zealand, so it opens in millimetres; Settings ▸ Units ▸ Default units switches to feet, inches and sixteenths for older drawings. It runs on Android 7.0 or later and works offline. Stairs, Concrete and Check Square are free. Baluster Spacing, Stud Counter, Running Measurements (marks off one tape, read aloud with Speak), Gravel, Pitch and Dumpy Level are among the other 13, which unlock with a weekly subscription that starts with a 3-day free trial, or a one-time lifetime unlock; Google Play shows the prices in your currency. It doesn't do winders, landings, rafter cuts or roof area. Quick sums in a browser: all the construction calculators. Other countries and trades: calculators by trade and country.

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Codes and sources

Checked on 1 November 2026. These are England's documents; building control, your drawings and the makers' guides decide what a particular job needs.

Approved Document K, 2013 edition (PDF), via GOV.UK: Table 1.1, paragraphs 1.9, 1.11, 1.39, 1.41 and 3.3, Diagram 3.1.
Approved Document A, Structure (PDF), section 2B: span tables by TRADA.
Approved Document H, 2015 edition (PDF): H3 paragraph 2.3 (paving) and 3.15 (rainwater drains).
West Fraser FAQs: CaberFloor joist centres.
Heidelberg Materials 40N Concrete data sheet (PDF): 0.008 m³ per MaxiPack20.

Which construction calculations come up on a UK build?