Formula used
- Total rise: R = vertical height from ground to deck.
- Feasible riser count: choose N such that R / N stays between your min and max riser limits.
- Selected risers: among feasible N, pick the one closest to your desired riser height.
- Actual riser height: h = R / N.
- Treads: if the deck is the top landing, T = N − 1; otherwise T = N.
- Total run: Run = T × tread_depth.
- Stringer length: L = √(R² + Run²).
- Angle: θ = arctan(R / Run).
- Proportion check: 2R + T uses 2h + tread_depth as a comfort indicator.
Always confirm local building requirements for outdoor stairs, guards, and landings.
How to use this calculator
- Measure the vertical rise from finished ground to the deck surface.
- Pick your unit system and enter a comfortable desired riser height.
- Set minimum and maximum riser limits for safety and consistency.
- Enter tread depth to estimate run, angle, and stringer length.
- Press Calculate and review counts, heights, and notes.
- Use CSV or PDF to save the summary.
Example data table
| Units | Total rise | Desired riser | Min–Max riser | Tread depth | Risers | Riser height | Treads | Total run |
|---|---|---|---|---|---|---|---|---|
| mm | 900 | 170 | 140–200 | 280 | 5 | 180.0 | 4 | 1120 |
| mm | 760 | 165 | 140–200 | 275 | 5 | 152.0 | 4 | 1100 |
| in | 36 | 7 | 5.5–7.875 | 11 | 5 | 7.200 | 4 | 44.000 |
Examples are illustrative; adjust limits and tread depth to match your design.
Riser count selection and consistency
Outdoor steps feel safest when every riser matches closely. The calculator tests all riser counts where the actual riser height stays within your minimum and maximum limits. It then chooses the count closest to your desired target, helping avoid a final “odd” step caused by early rounding. For example, a 900 mm rise yields 5 risers at 180 mm, or 6 risers at 150 mm each.
Total run, angle, and space planning
Garden layouts often limit available footprint. Total run equals tread count multiplied by tread depth, and the stair angle is derived from the rise-to-run relationship. A longer run lowers the angle and can improve comfort, but it also consumes more space near beds, paths, and gates. Tighter sites may require more risers or shorter treads.
Deck-as-landing option and tread count
Many decks serve as the top landing, so the walking surfaces are usually one fewer than the risers. Selecting “deck as top tread” sets treads to risers minus one, matching layouts where the deck surface replaces the last tread board. Choose the other option for a separate top platform. This changes total run and the number of tread boards.
Stringer length estimate for material takeoff
Stringer length is estimated using straight-line geometry from total rise and total run. Use it for quick material takeoff, transport planning, and a sensible waste margin. It does not include nosing overhang, skirt boards, or trimming for sloped grade, so keep extra length for site adjustments. Mark rises and treads from the computed values for uniform layout.
Comfort check using 2R + T
The proportion check uses 2R + T, where R is the calculated riser height and T is tread depth. Mid-range results often feel natural; low values can feel steep, while high values can feel overly long. Treat the note as guidance for tuning tread depth or step count. Small tweaks, like adding 10 mm tread depth, can shift the check noticeably on shallow garden stairs.
FAQs
1) How do I measure total rise accurately?
Measure from finished ground level to the finished deck surface where you will step off. Use a long level or straight board to avoid measuring to uneven soil or temporary grading.
2) Should the deck surface count as the top tread?
Choose “Yes” when the deck is the final landing you step onto, which makes treads one fewer than risers. Choose “No” when you are building a separate top platform or landing board.
3) What if the result is outside my min and max riser limits?
Widen the limits slightly, adjust the desired riser target, or recheck the total rise measurement. Small measurement changes can shift the feasible riser counts and bring the calculated riser height into range.
4) How should I choose tread depth for garden steps?
Pick a depth that matches your available space and walking comfort. Deeper treads reduce the stair angle but increase total run. Keep the tread depth consistent so footing stays predictable in wet or muddy areas.
5) Does rounding change the recommended riser count?
No. Rounding only changes the displayed riser height. The calculator selects riser count using exact values, then applies rounding for easier marking or reporting.
6) How do the CSV and PDF downloads work?
Run a calculation first. Then click CSV or PDF to download a summary of your latest inputs and outputs, suitable for sharing or saving with your project notes.