Stair Stringer Calculator – Calculate Stair Dimensions

A Stair Stringer Calculator helps you determine what sizes you need to build a staircase, including how many steps, the step height or riser, the horizontal depth or tread, plus the length of the stair stringer.

Whether you are building outdoor wooden stairs, a deck staircase or indoor steps you need to determine what measurements you need. This calculator estimates a staircase layout, including the length of a stair stringer.
How to Use the Stair Stringer Calculator

We have created a set of steps to help you calculate your stair stringer size.

1. Enter Total Rise: The distance between the lower floor or landing and the top or landing

2. Enter Desired Riser Height: The height you need your riser to be - this should follow building regulations

3. Enter Tread Depth: The horizontal depth of your stair tread

4. Calculate: Click the calculate button to estimate the number of steps, the actual riser height, total horizontal run and length of the stringer

5. Review the Results: All the results use the numbers you enter to help you plan your staircase

6. Always go over all your measurements to ensure accuracy before you cut the stringer

Stair Stringer Calculator Formula

There are several formulas used by the calculator.

1. Number of Risers

Number of risers = Total rise / Desired riser height

This should give a whole number, you might need to round this number up or down.

2. Actual Riser Height

Actual riser height = Total rise / Number of risers

3. Total Horizontal Run

Total run = Number of treads x Tread depth

Typically in a staircase, where the landing is a feature you will have one less treads than the number of risers.

4. Stringer Length

Stringer length = √(Total rise² + Total run²)

Example calculation

Let us suppose we want to make a staircase with the following measurements:

• Total rise: 96 inches
• Desired riser height: 7.5 inches
• Tread depth: 10 inches
First we calculate the Number of Risers:

96 / 7.5 = 96 ÷ 7.5 = 12.8 risers

Let us round this up to 13 risers. We then calculate the Actual Riser Height:

96 / 13 = 96 ÷ 13 = 7.38 inches per riser

Now let us calculate the Total Run:

There will be 13 risers there will be 12 treads;

12 x 10 = 12 × 10 = 120 inches

Finally work out the Stringer Length:

Stringer length = √(96² + 120²)

Stringer length = √(9,216 + 14,400)
Stringer length = √23,616 ≈ 153.68 inches

So we have estimated the diagonal dimension of the staircase as being 153.68 inches or approximately 12.81 feet. Note that the calculation includes a saw cut for each step, including the bottom steps. You will always want to have some allowance for the cutting and sawing. You should also check the finish layout before you cut.

Understanding your result

There are several numbers displayed by this calculator that you will want to be aware of:

• The Number of Risers is a measurement that represents how many vertical rises there are in the whole length of your staircase.
• The Riser Height is how high your rises are, this needs to be uniform for every step.
• The Tread Depth is the horizontal depth of each stair tread.
• The Total Run is how much horizontal room the staircase will occupy.
• The Stringer Length is the estimated distance of the diagonal length of the staircase.

These all help you understand and plan out whether you have the space for a staircase and whether it will match your expectations in terms of use.
Factors that affect the result

There are several factors that influence the calculation and result of a Stair

Stringer Calculator:

Total Rise: More vertical height will require more steps or taller risers.
Riser Height: Taller steps means fewer steps and a shorter horizontal length occupied.

Tread Depth: Deeper treads increase the overall horizontal distance occupied by the staircase.

Available space: Always a factor in building a staircase.

The thickness of materials: The thickness of the treads and cuts required in the stringer will impact on the final product. Different materials offer different strength and durability characteristics.

Building Regulations: In your area, there may be regulations on the height of a stair riser, depth of treads, whether and type of handrail is to be installed plus any requirements for a landing at the top or bottom of a staircase.

Benefits and Practical Uses of the Calculator

A Stair Stringer Calculator has a number of benefits and practical applications:

It saves time: Quickly estimating what sizes you will need.
Helps you understand how the staircase can fit into the building: Including the space it will take up.

Save money: Helping you ensure you know how much materials you will be needing and want to purchase.

Improves Consistency: Helps to ensure that the consistent step height and depths are achieved.

Useful for a number of situations: Whether you are a homeowner, a carpenter, a builder or a contractor you can use the calculator when building a staircase indoors or outdoors.

Accuracy, Assumptions and Limitations of the Stair Stringer Calculator

The calculator provides you with an estimated calculation based on the input information. The accuracy of the estimation is dependent on what measurements you take:

The basic calculation for Stringer Length is based on the simple diagonal length and ignores the sawing and notching that will be required. Material thickness is ignored, as is any adjustment in floor levels. The final calculation for the stringer length ignores any adjustment on the upper landing.

The calculation uses a formula that assumes a common staircase where a landing is a feature; the number of treads will therefore be one of less than the number of riser steps. These are assumed unless you specify that you want to make a different style of staircase. Always understand and follow relevant building regulations and double check the final layout of the stringer to verify it matches your intended design. Also make sure that you understand how such a stringer would integrate into a larger structural staircase. Always follow the relevant building plans and seek the advice of a professional if unsure.

Frequently Asked Questions (FAQs)

1. What is a stair stringer?

This is a staircase component that supports the treads and risers. Stair stringers are commonly constructed from timber or metal, but can also be formed from concrete depending on the design of the staircase.

2. How do I calculate stair stringer length?

Calculate the total vertical rise and horizontal run, square both and add together, square root the result to provide an estimate of the length of a stair stringer.

3. How many steps do I need for a staircase?

To find out how many steps you need for a staircase divide your total rise by your estimated desired riser height and round to a suitable whole number. Divide your total rise again by this number to give you the actual riser height.

4. What is the ideal stair riser height?

The stair riser height can depend on where you are building the staircase or stairs. Many residential stair designs have risers that are approximately 7 to 7.75 inches, but you should always confirm with local building regulations.

5. What is the standard tread depth for stairs?

A tread depth of approximately 10 to 11 inches is often used for a residential staircase; however, this can vary and is always best to double check with your local building regulations.

6. Do I need to include the upper landing when calculating stringer length?

The upper landing will determine the landing point of your staircase. You will need to measure the total rise to the finished upper floor including the landing and any adjustments for the connection layout when laying out the stair stringer.

7. Can I use this calculator for outdoor deck stairs?

Yes, you can use the calculator for a number of projects including estimating outdoor deck stairs, garden steps etc. Note that you will need to incorporate suitable materials, stable foundation and always follow local regulations for your outdoor staircase project.