Stair Calculator
| Exact Riser Height | - |
| Total Run (Horizontal) | - |
| Stringer Length | - |
| Stair Angle | - |
| Comfort Check (Blondel) | - |
How Stair Dimensions Are Calculated
The calculator divides the total rise (floor-to-floor height) by your chosen maximum riser height, rounding up to a whole number of steps, then divides the total rise evenly across that many steps to get the exact riser height - keeping every step the same, which is important for safety. It also finds the stringer length (the diagonal support board) using the Pythagorean theorem, and checks your riser-plus-tread total against the classic Blondel comfort formula used by architects.
How to Use This Stair Calculator
- Fill in the input fields on the left with your own numbers - every field is pre-filled with a sample value so you can see the layout working immediately.
- Click the Calculate button to instantly generate your result in the panel on the right.
- Read your result, along with the supporting breakdown table and chart, to understand not just the answer but how it was reached.
- Change any value and click Calculate again as many times as you like - there is no limit on how often you can use the stair calculator, and nothing is saved or sent anywhere.
Frequently Asked Questions
What is a comfortable riser height?
Most residential building codes recommend a riser height between about 15 cm and 19.7 cm (roughly 6 to 7.75 inches) for comfortable, safe stairs.
Why does the tread depth matter?
A common rule of thumb (the Blondel formula) is that 2 × riser height + tread depth should land close to 63-65 cm (about 25 inches) for a natural, comfortable stride - too steep feels like a ladder, too shallow makes you shuffle.
What is the stringer length used for?
The stringer is the diagonal board that supports the treads and risers; knowing its length in advance helps you buy the correct length of lumber or steel before cutting.
Tips for Getting Accurate Results from the Stair Calculator
- Double-check every input before calculating - a misplaced decimal point or wrong unit is the most common cause of an unexpected result.
- Make sure the units shown next to each field (kg, cm, %, hours, and so on) match the units of the number you are typing in; convert first if they don't.
- If a result looks off, try the calculation with round, simple numbers first (like 10 or 100) to confirm the tool is behaving the way you expect, then switch back to your real figures.
- Bookmark or save this page if you use the stair calculator regularly, since all calculations run instantly in your browser with no sign-up required.
How to Print or Save This Stair Calculator as a PDF
- Fill in your values and click Calculate.
- Click the Print link at the top of the page.
- In the print dialog that opens, choose "Save as PDF" as the destination (instead of a physical printer) to download a PDF copy.
- Make sure "Background graphics" is turned on in the print settings so the colors print exactly as shown on screen.
- Click Save or Print - only the stair calculator's inputs and results are included; the site navigation, sidebar, footer, and the theory/FAQ sections below are automatically left out to keep the printout clean and focused.
More Frequently Asked Questions
Is this stair calculator free to use?
Yes, completely free, with no registration, download, or watermark - just enter your numbers and get an instant result.
Does this calculator work on mobile phones?
Yes, the layout automatically adjusts for phones and tablets, so you can use the stair calculator on any device with a modern web browser.
Is my data stored or sent anywhere?
No - every calculation on this page runs locally in your own browser using JavaScript; nothing you type is uploaded, logged, or stored on any server.
Can I rely on this for professional or legal decisions?
This tool is designed to give a fast, well-informed estimate for everyday use. For decisions with financial, legal, medical, or safety consequences, always confirm the figures with a qualified professional in that field.