**Definition of stair run: **Stair run is
the total horizontal distance traveled by a passenger using the staircase, from
the first riser face to the last riser.

**Definition of stair rise**: The rise of a stairway is
the total vertical height of a stairway between the running surface, which is
just before the first stair tread or walk, and the beginning of the horizontal
tread surface at the top of the staircase.

Working out stairs can sometimes be a bit hectic topic . In this article we are going to look at how to calculate stairs(riser, tread ,slope) the quick and easy way to work out your stair requirements.

**How to Calculate Stairs:**

**Figure- 1: Staircase with details**

In this example, let me consider a staircase with
details shown in Figure 1.Basically, in architectural drawings , the levels such as **FFL** (floor finish level) or **SSL **(structural slab level) are already provided as per the design. In figure-1, i have shown two levels ,one at floor(+4000 mm) and other at landing(+1900 mm). I have shown these levels to give an idea when after completing your degrees in civil engineering ,you will work on site construction and it will help you as well.

**1. Calculate
the flight **

Here i have considered two levels as you can see in the figure 1 above

Floor level= 1900 mm

Landing level= 4000 mm

Flight = 4000
- 1900 = 2100mm

So, staircase is 2100 mm high.

**2.Calculate
the number of steps that will be needed:**

Considering an
ideal riser of 150 mm, the height of the space is divided by the height of each
step.

2100/150= **14
steps**

**3. Calculate
the height of each riser and width of each tread:**

The height of the space is divided by the number
of steps that we have just obtained:

2100/14
= **150 mm height for each riser**

So as per standard, we are providing 300 mm as
tread length.

Number of
Tread = Length of Stair/One number of Tread

= 3800/300

= **13 No.s**

we know that
:(**T+2R=600**)

so, T +
2x150=600mm

T=600-300 =**300mm (width of tread)**

**Scope of the formula:**

Nicolas Francois Blondel (1675–1683) was the first known
person to establish the ergonomic relationship of tread and riser dimensions in
the last volume of his Cours d'architecture.

He specified that 2 x riser + tread = step length.

Ideal requirements of stair

Step proportions:

T + 2R = 60-64 cm

T x R= 400-426 cm

2T + R = 40-45 cm

Standard values:

For residential building: T = 22-27 cm, R = 15-17 cm

For public building: T = 30 cm, R = ≤15 cm

**How to work out the
angle or slope of the stair?**

**Figure- 2: Slope of staircase**

In order to work out our stair angle we can use a
bit of basic trigonometry refer figure-2

Total Run =
3800mm

Tan=opposite/adjacent

Opposite /
Adjacent =

1940 / 3800 =
0.51

Inverse Tangent of 0.51 =27 degrees

**The angle or slope of staircase = 27 degrees**

As per IS 456, the slope or pitch of stair should be between 25 degrees to 40 degrees.

**Internal
staircases should:**

One flight between landings shall be designed for maximum number of people occupying that floor.

Not
have any fire risk spaces opening directly on to staircase.

Have
their external exit door at ground level, and should open directly to open
spaces, or large lobby, if necessary.

Main
stairs to be continuous from ground to terrace.

Should
not have any combustible decoration.

Have clearly visible exit signs.

Show individual floors.

Be of non combustible material.

Be a self contained unit, enclosed, and with one side made of external wall.

Not be arranged around a lift shaft.

Not be of hollow combustible construction.

Not have gas piping or electrical panels along the stairway.

Can have ducting if it provides one hour of fire rating.

**It has dimensions as:**

minimum staircase width = 1.5 m

minimum tread width = 300mm

maximum riser height = 150mm

maximum 15 risers per flight

handrail height = 1.0m

minimum head room = 2.2m

**External
staircases are desirable for high rise buildings, and when provided shall
comply to the following:**

**Some dimensions as:**

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