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According to OSHA, to safely reach the roof of a 17-21 feet tall 2 story house, you’ll need at-least 28 feet long extension ladder or a 24 feet straight ladder. Ladder rungs should clean, tight and safe. Never overload a ladder, never stand on the top rung, consider user’s and tool’s weight when choosing the right ladder for the job.

  • A ladder is a tool used to climb up and down from high places.
  • We use the Pythagoras theorem to calculate the height of the ladder to use.
  • 4 to 1 rule always applies.
  • Extension ladders must rise 3 feet higher than the supportive structure.
  • A step ladder is preferred in a one-story house.
  • An extension ladder is recommended on a two-story house.

A ladder is a tool used to climb up and down from high places. It consists of steps for climbing up the ladder and two side rungs to support the steps. It could be made of wood, aluminum, or fiberglass. A ladder could either be self-supporting or non-supporting. There are different types of ladders, namely:

  • Fixed Ladders
  • Portable Ladders

Fixed Ladders

Fixed ladders are permanently attached to a supporting structure such as a building, wall, or any other permanent structure.

Portable Ladders

Portable ladders can be carried from one place to another as the user desires. In other words, not fixed in a permanent position.

The height of a ladder to be used varies; let’s consider these scenarios. You are using a ladder to reach up to a house roof, or maybe you are using a ladder to reach out to a 2-story home. In both situations, you will need a different type of ladder, both in height and type, depending on the work to be done.

Understanding the Math Behind Determining the Ideal Height of a Ladder for 2-Story House

The problem can solved using 2 math formulas. Let’s dive into some calculations;

Formula 1: A2 + B2 = C2

what size ladder for 2 story house math

To calculate the minimum required height of the ladder, we use the simple calculation methods.

Let’s consider this example.

You are required to climb a 12 feet house and the estimated distance between the base of the ladder and the wall is 3 feet. What is the minimum required height of the ladder?


(A^2) + (B^2) = (C^2)

It is always important to remember the ladder angle rule while setting up a ladder, which is 75 degrees.


A = 12

B = 12/4 = 3 (using the 4 to 1 ladder angle rule)

Using the formula;

(A^2) + (B^2) = C^2

(12^2) + (3^2) = C^2


(C^2) = (144 + 9) = 153

√153 = 12.36

Now, we must add the 3 foot more to make sure the ladder rises properly according to the OSHA standard.

So, the answer is, 16 feet is the ideal ladder length to safely climb a 12 feet tall house using a straight ladder. In case of extension ladder, the ideal length of the ladder would be 19 feet considering the OSHA guideline of minimum 3 feet overlap for ladders below 36 feet and 4 feet overlap for 40 feet extension ladders and above.

Formula 2: H + A + 3= L

In this formula, (h) is the height of the supporting wall, (a) is the angle size, and (L) is the length of the ladder.

From the example;

Height of the house (h) = 12 feet
Distance between ladder and the Supporting wall (a) = 3 feet

(12+ 3+3) = 18 feet

When using an extension ladder, it is essential to take note of the extension rung and overlap. Which is 3 feet for up to 36 feet extension ladder and 4 feet for above 36 feet extension ladders.

What Size Ladder for 1 Story House

Before diving into the math behind choosing the best ladders for using in a one-story house we must understand what is a one-story house and how the authorities see it.

What is a 1 Story House

A one-story house is a house that has only one level of the building, excluding the basement. It is commonly referred to as a bungalow. Also known as a single-story.

How Tall is a 1 Story House & What does the Height of House Mean?

An average one-story building is 10-15 feet tall or instead 3-5 meters tall. In this case, the height is calculated as the total distance from the ground floor to the highest point of the house, the roof.

Key Characteristics of a 1 Story House

  • A 1 story building should have a strong foundation with a story that is 2 meters below the ground.
  • The one-story house should have 9 feet length from the ground to the ceiling and a one-foot floor thickness.
  • Ideal floor to floor height of a single-story house should be about 9 to 11 foot.
  • Height of the interior is about 8 to 10 foot.

How to Calculate the Best Ladder Size for 1 Story House

Let’s use the example below;

what size ladder for 1 story house

When calculating the best ladder to use, we use the Pythagorean Theorem:


(A^2) + (B^2) = (C^2)

Let (S) be 4 feet

And (L) the height to climb the roof 11 feet

To find the length of the required ladder, we substitute the values of S and L.

Using the formula;

(S^2) + (L^2) = C^2

(4^2) + (11^2) = C^2


(C^2) = (16 + 121) = 137

√137 = 11.71 foot

So, what size ladder for 1 story house? The answer is, 15 foot if it’s a straight ladder and 18 foot in case it’s an extension ladder.

Best Ladder for 1 Story House

For works such as painting, cleaning gutters, cleaning windows, and repairs, you would need to use either an extension ladder of roughly 3-4 meters or, most preferable, a-frame step ladder.

An extension ladder of approximately 14-17 feet would be ideal when reaching the roof or doing roof repairs of a 1 story house.

Safety Checklist When Using a Ladder on a 1 Story House

  • Always make sure to position the ladder at the right angle following the ladder angle rule.
  • Always select the right ladder for the right job.
  • Use a ladder tray paint when painting.
  • Use a ladder tray when painting.
  • Always climb the ladder using two hands.
  • Never overreach.
  • Do not position a ladder near electricity poles. Always maintain minimum 10 foot distance from electric wires and poles.
  • Do not leave a step ladder unattended.

What Size Ladder for 2 Story House

Understanding the core foundations of ladder size measurement math and what a two story house will help us determining the best ladder size for using on a 2 story house.

What is a 2 Story House

The houses consisting of two building levels, the ground floor, and the top floor, are known as two-story houses. It is also known as a double-story houses.

How Tall is a 2 Story House & What does the Height of House Mean?

While height measurements of two-story houses could vary from one to another, average height is about 16-25 foot. Each floor should have the floor to floor distance of between 8-12 feet. However, this could vary depending on the floor thickness, ceiling height, and height allowances for different levels. The ceiling height should be at least 8 feet.

Key Characteristics of a 2 Story House

  • The area coverage could vary depending on the plot of land. This will also affect the design of the house.
  • Each story should be at least 7 -11 feet tall.

How to Calculate the Best Ladder Size for 2 Story House

what size ladder for 2 story house graph

Let’s do some calculations.


  • a is the length of the wall = 16 feet
  • b is the length between the wall and the base of the ladder = 4 feet
  • c is the required height of the ladder.

Using Pythagoras theorem;


(A^2) + (B^2) = (C^2)

Let (a) the height of the wall = 16 foot

And (b) the length between the wall and the base of the ladder = 4 foot

To find the required height of the ladder, (c)

Using the formula;

(a^2) + (b^2) = c^2

(16^2) + (4^2) = c^2


(C^2) = (256 + 16) = 272

√272 = 16.50 foot

So, what size ladder for 2 story house? The answer is, 20.50 foot if it’s a straight ladder and 23.50 foot in case it’s an extension ladder, since an extension ladder needs to extend 3 feet above the supporting structure.

Best Ladder for 2 Story House

It is often asked which is the best ladder to use on a two-story house, but no specific ladder can be termed as best. It all depends on the kind of work you need to do with the ladder.

For works such as reaching the roof, cleaning gutters, repairs, and painting, an extension ladder of 25 foot would be ideal. Remember, the house’s height is also a significant factor to consider when choosing a suitable ladder.

A 22 foot step ladder with work platform could equally do the job when cleaning windows.

What Size Ladder for Multi Story House

Method of calculating the what size ladder for multi story house is same as calculating for the double story house. Get the height of the supporting wall, distance between wall and ladder base, use the formula, A2 + B2 = C2 where (a) is the wall’s height, (b) is the distance between wall and ladder’s base.

what size ladder for 3 story house

Follow the Extension Ladder’s Height Restrictions Table below while using an extension ladder for multi-story houses:

Ladder Height (Feet)Maximum Reach (Feet)Highest Point Ladder Will Touch (Feet)
20'19'9' to 13'
24'23'13' to 17'
28'27'17' to 21'
32'31'21' to 25'
36'34'25' to 28'
40'37'28' to 31'

Keep in mind, OSHA recommends minimum 4 feet overlap when the extension ladder is longer than 40 foot.

While selecting the right type of ladder is crucial, choosing the right kind of material is also equally important.
For a two-story house, an extension ladder would be ideal. It has an overlap allowing for extension up the home and offering generous support.

It is often asked, which is the best material to use on ladders? The following will help you decide which best suits your needs.

Fiberglass Ladders

Fiberglass is a sturdy and robust material. It lasts longer than all other materials used to produce ladders. It is considered best compared to wood or aluminum, although it’s a bit pricey.

You do not have to worry about adverse weather conditions since it is suitable to use in any weather conditions. It’s also a poor conductor of electricity, and that makes it friendly to operate around electricity.

Aluminum Ladders

Aluminum is the most common material used to make ladders because it is cheap and easy to carry around. However, aluminum ladders are not as durable as fiberglass ladders since they cannot withstand heat. Aluminum is a great conductor of electricity. You can not use an aluminum ladder anywhere near an electric hazard. You also have to be watchful about heat around the working area because aluminum is prone to heat damage.

Read my detailed blog on aluminum vs fiberglass ladders and when aluminum is better than fiberglass.

When choosing a ladder, it is always important to consider two things; the height and the reach. This, however, depends on the type of ladder in use. Assume you want to reach a 12 feet building; you need an 8 feet step ladder. The safe standing height is also a significant consideration when using any ladder. According to the regulations, You should stand approximately 3 feet or 1 meter from the top of the ladder, which is 2-3 steps down.

Step Ladders Size Chart

Height of the HouseCorrect Height of the Step LadderSafe Standing Height
10 feet 4 inch6 feet3 feet 9 inch
12 feet 1 inch8 feet5 feet 6 inch
14 feet 6 inch10 feet7 feet 10 inch
16 feet 2 inch12 feet9 feet 7 inch
18 feet 3 inch14 feet11 feet 8 inch

With extension ladders, we have to consider the overlap as well as the maximum overlap allowed. An extension ladder should be positioned right. Since an extension ladder needs to extend minimum 3 feet above the supporting structure, you must add 3 feet to the height of the ladder.

Extension Ladders Size Chart

Correct Ladder SizeMaximum Reach of the LadderSafe Standing Height
16 feet10 to 13 feet6 to 8 feet
18 feet14 to 17 feet11 to 14 feet
26 feet20 to 23 feet17 to 20 feet
30 feet24 to 26 feet21 to 23 feet
34 feet27 to 30 feet24 to 27 feet
36 feet31 to 33 feet28 to 30 feet

According to the Occupational Standards Health Authority, each section of an extension ladder should not exceed 20 feet.

A two-section extension made of wood and a three-section extension ladder made of metal should have a maximum length of 60 feet. In contrast, a two-section extension ladder made of metal should have a maximum height of 48 feet.

The minimum overlap required varies depending on the length of the ladder.

Extension Ladder size (Foot) Minimum Overlap (Inches)
0 to 32'36"
33' to 36'46"
37' to 48'58"
49' to 60'70"

A step ladder can perform various tasks such as painting, reaching higher shelves, among others. The height varies in all these places, and therefore one should select the best ladder.

When selecting a step ladder, always choose a ladder that is 4 feet above the height you are working with. For example, when the supporting wall is 6 feet, select a 10 feet tall step ladder.

OSHA recommended size chart for step ladders:

Required Height to Climb (Feet) Step Ladder Height (Feet)
  • Always follow the 4 to 1 ladder angle rule when setting up a ladder.
  • Always select the right ladder for the right job.
  • Always read ladder instructions before using a ladder.
  • Climb up and down a ladder using two hands, ensuring three point connection.
  • Always choose the right ladder for the correct type of building.
  • Always label the malfunctioning ladder and DO NOT use it.

I cannot emphasize more the importance of choosing the right ladder for the right job. Getting the best ladders not only helps in improving the efficiency of work done but also helps in ensuring the safety of the user as well as save on time.

Therefore, it is vital to consult and research widely before purchasing a ladder. Not all types of the ladder are suitable for every kinds of jobs.

Step Ladders

Step Ladder is used to perform simple tasks such as painting, reaching for shelves, or changing light bulbs.

Best Choice portable folding step ladder is a good example of a step ladder.

Straight Ladders

Straight ladder is mostly used to perform basic tasks such as painting, cleaning gutters.

It is non-supporting and gets its support from leaning on the supporting structure.

Werner (D6212-1) ladder is a good example of a straight ladder.

Extension Ladders

Extension ladders are mainly used to perform duties such as cleaning the windows, cleaning the gutters, and roof repairs on much higher places.

Ideal for cleaning gutters and windows of a 2 story house. Taller extension ladders can be used to clean windows and gutters of multi-story houses.

Multipurpose Ladders

Multipurpose ladders, as the name suggests, are used to perform multiple functions. It Could be used as a step ladder when folded, an extension ladder, a scaffold ladder, and a straight ladder.

It is generally used to meet all your ladder needs, from painting to cleaning gutters and repairing roofs.

Step Stool

Step stools help to reach heights that are just off the ground but not too high. It is about 1-2 feet tall.

Kitchen, closet and library etc. have the most practical use of step stools.

Delxo aluminum 3 step stool can be an ideal step stool for your everyday needs in a 2-story house.

Fire Escape Ladders

As the name suggests, fire escape ladders are mostly for safety. They are attached to multi-story buildings, to help in case of a fire emergency.

Avoid wooden ladders and make sure your fire escape ladder has anti-slip rungs while getting the best fire escape ladders.

Attic Ladders

Attic ladders are used to access attics. Usually an attic ladder has insulated doors to prevent heat from escaping the house. Here’s my guide on The Best Attic Ladders For Money.

Telescopic Ladders

Telescoping ladders have a unique feature which allows the ladder to compress in less storage space. It can also be elongated to offer access to higher places.

I like Good Life professional telescopic ladders for their feature and durability.

Flexible Ladders

Flexible ladders are adjustable and can be rolled up easily. They are mostly used for outdoor activities or in case of emergencies.

Platform Trestle Ladders

Platform trestle ladders can be helpful for painting and cleaning gutters in exterior walls. They usually have a supporting platform attached on top of the A-shaped ladder for support.

Having a ladder work platform can increase the productivity and safety of your work.

A- Frame Ladders

A-frame ladders are similar to step ladders but mostly used in garages to access high places.

Portable Ladders

Portable ladders with are easy to move around using the rolling wheels. Rolling portable ladders are mostly used in warehouse and workshop settings.

Articulated Ladders

Articulated ladders have several hinges which allows it to be used as a single ladder, extension ladder, step ladder, among others.

Last Words

Not every ladder is suitable for any kind of job. Therefore, we should strive to be informed about the different types of ladders and use them correctly. Prevention is always better than cure.

Hope I’ve clearly answered your questions on what size ladder for 1 story house, what size ladder for 2 story house and what size ladder for multi story house. You can now claim yourself a master of measuring the safest ladder angle and selecting the correct ladder for the right job.


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