This app was designed by a Red Seal certified carpenter for carpenters. If you build formwork for concrete stairs on commercial construction sites, this app is meant for you. No ads, no data collection.

Whether you're dealing with metric or imperial, this calculator will take dimensions that are already specified on your site drawings and provide you with the following information to assist you with your layout:

- Length of your support rafters for your sloped soffit;
- Horizontal distance from your first riser to the base of your support rafter as well as the bottom turning point of the concrete soffit;
- Horizontal distance from your top riser to the top of your support rafter as well as the top turning point of the concrete soffit;
- Whether the above mentioned points are situated in the uphill or downhill direction from their respective risers;
- The unit of rise per step, along with warning messages if the unit rise or unit run exceed allowable limits for public stairs according to the most current British Columbia Building Code;
- Concrete volume for stairs and landings;
- The elevation of the sloped concrete soffit at a user-specified distance away from the top of the stair, referred to as "wall height under stair;"
- The exact measurements between stringer layout points on your reverse stringer, which produces the most accurate result for long flights of stairs compared to stepping off your rise and run with a framing square and stair gauges. This can also be used to check the total diagonal measurement of your stair run, to confirm that your overall layout is correct;
- Stringer/rise calculation support for up to 6 flights of stairs at once, for drawings that specify a total stair rise across multiple landings rather than per each flight.

You can input feet-inches-fractions, decimal feet, decimal inches, or a combination of decimals and whole numbers.
Imperial results will always appear as feet-inches-fractions, rounded to the nearest 16th of an inch.

You can input meters-millimeters or decimal meters.
Metric results will always appear in millimeters, rounded to the nearest whole number.

I have also included visual guides to provide an easy reference for what each function calculates, which are accessible from the main page of the app as well as on each function's own page.

How will this app speed up your stair formwork layout? Let's compare the standard tried-and-true method with the information you'll get from this app.

The standard method:
Mark out your first 3 risers and treads on the wall.
Extend the treads by your rake/nosing.
Square down from your rake points the distance of your stair throat.
Add the plywood thickness to get to your rafter point.
Repeat the entire process with your top 3 risers and treads, rake, stair throat, and plywood thickness.
Chalk the line of your rafter.
Measure the length of your rafter chalk line and start cutting.
Install your rafters once you've finished cutting them.

All that to figure out your rafter and layout.

Now for the app method:
The app immediately tells you how long to cut your rafter without requiring any layout, as well as the mitre angles for the top and bottom plumb/level cuts. Your apprentice/helper can start cutting the rafters before you've even drawn a single layout line.
Mark the first riser on the wall.
Measure over from the first riser and mark the bottom tip of the rafter on the wall.
Mark the top riser on the wall.
Measure over from the top riser and mark the top tip of the rafter on the wall.
Line up your (already pre-cut) rafter with your layout marks and start installing your formwork.

If you subscribe to the standard method, this app will save you hours of work.