A 138" floor-to-floor stair needs 18 risers at 7-11/16" and 17 treads: a 170" run on 10" treads, cut from 20 ft 2x12s with 5-3/16" of throat. Gentler: 19 risers at 7-1/4" on 11" treads, a 198" run (2R + T = 25.5").
finished to finished
fewest legal
nosing to nosing
3/4–1-1/4 under 11″
DCA 6 max 18
138" total rise
Hook the tape once at mark 0, where the bottom riser line meets the top edge of the 2x12, and pencil every mark from that same hook. Each step is 12-5/8"− along the edge; marks are rounded once each, so nothing drifts.
| Done | # | Mark | Tape | Decimal | mm |
|---|---|---|---|---|---|
| 0 | Bottom riser line | 0" | 0.000" | 0 mm | |
| 1 | Tread 1 nose | 12-5/8"− | 12.601" | 320 mm | |
| 2 | Tread 2 nose | 25-3/16" | 25.201" | 640 mm | |
| 3 | Tread 3 nose | 37-13/16" | 37.802" | 960 mm | |
| 4 | Tread 4 nose | 50-3/8"+ | 50.403" | 1280 mm | |
| 5 | Tread 5 nose | 63" | 63.004" | 1600 mm | |
| 6 | Tread 6 nose | 75-5/8"− | 75.604" | 1920 mm | |
| 7 | Tread 7 nose | 88-3/16"+ | 88.205" | 2240 mm | |
| 8 | Tread 8 nose | 100-13/16" | 100.806" | 2560 mm | |
| 9 | Tread 9 nose | 113-7/16"− | 113.406" | 2881 mm | |
| 10 | Tread 10 nose | 126" | 126.007" | 3201 mm | |
| 11 | Tread 11 nose | 138-5/8"− | 138.608" | 3521 mm | |
| 12 | Tread 12 nose | 151-3/16"+ | 151.208" | 3841 mm | |
| 13 | Tread 13 nose | 163-13/16" | 163.809" | 4161 mm | |
| 14 | Tread 14 nose | 176-7/16"− | 176.410" | 4481 mm | |
| 15 | Tread 15 nose | 189" | 189.011" | 4801 mm | |
| 16 | Tread 16 nose | 201-5/8" | 201.611" | 5121 mm | |
| 17 | Top plumb cut | 214-3/16"+ | 214.212" | 5441 mm |
Then from mark 0 measure 6-5/8" down the bottom riser line and square across for the level heel cut.
Shortest run, steepest legal stair
Gentler climb, longer run
Floor to floor = ceiling + joists + subfloor. With 12-1/2" of floor framing and ceiling, the stairwell opening over Option A starts 49-3/8" from the bottom riser and runs 10' 5/8" for 6'-8" of headroom.
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| 0 | Bottom riser line | 0" | 0.000" | 0 mm | 0" |
|---|---|---|---|---|---|
| 1 | Tread 1 nose | 12-5/8"− | 12.601" | 320 mm | 1' 5/8" |
| 2 | Tread 2 nose | 25-3/16" | 25.201" | 640 mm | 2' 1-3/16" |
| 3 | Tread 3 nose | 37-13/16" | 37.802" | 960 mm | 3' 1-13/16" |
| 4 | Tread 4 nose | 50-3/8"+ | 50.403" | 1280 mm | 4' 2-3/8" |
| 5 | Tread 5 nose | 63" | 63.004" | 1600 mm | 5' 3" |
| 6 | Tread 6 nose | 75-5/8"− | 75.604" | 1920 mm | 6' 3-5/8" |
| 7 | Tread 7 nose | 88-3/16"+ | 88.205" | 2240 mm | 7' 4-3/16" |
| 8 | Tread 8 nose | 100-13/16" | 100.806" | 2560 mm | 8' 4-13/16" |
| 9 | Tread 9 nose | 113-7/16"− | 113.406" | 2881 mm | 9' 5-7/16" |
| 10 | Tread 10 nose | 126" | 126.007" | 3201 mm | 10' 6" |
| 11 | Tread 11 nose | 138-5/8"− | 138.608" | 3521 mm | 11' 6-5/8" |
| 12 | Tread 12 nose | 151-3/16"+ | 151.208" | 3841 mm | 12' 7-3/16" |
| 13 | Tread 13 nose | 163-13/16" | 163.809" | 4161 mm | 13' 7-13/16" |
| 14 | Tread 14 nose | 176-7/16"− | 176.410" | 4481 mm | 14' 8-7/16" |
| 15 | Tread 15 nose | 189" | 189.011" | 4801 mm | 15' 9" |
| 16 | Tread 16 nose | 201-5/8" | 201.611" | 5121 mm | 16' 9-5/8" |
| 17 | Top plumb cut | 214-3/16"+ | 214.212" | 5441 mm | 17' 10-3/16" |
Step-off 12-5/8"− (12.6007") · bottom cut 6-11/16" under 1" treads · last mark 17' 10-3/16" at the top plumb cut.
| 0 | Bottom riser line | 0" | 0.000" | 0 mm | 0" |
|---|---|---|---|---|---|
| 1 | Tread 1 nose | 13-3/16" | 13.182" | 335 mm | 1' 1-3/16" |
| 2 | Tread 2 nose | 26-3/8" | 26.363" | 670 mm | 2' 2-3/8" |
| 3 | Tread 3 nose | 39-9/16"− | 39.545" | 1004 mm | 3' 3-9/16" |
| 4 | Tread 4 nose | 52-3/4"− | 52.726" | 1339 mm | 4' 4-3/4" |
| 5 | Tread 5 nose | 65-15/16"− | 65.908" | 1674 mm | 5' 5-15/16" |
| 6 | Tread 6 nose | 79-1/16"+ | 79.089" | 2009 mm | 6' 7-1/16" |
| 7 | Tread 7 nose | 92-1/4"+ | 92.271" | 2344 mm | 7' 8-1/4" |
| 8 | Tread 8 nose | 105-7/16" | 105.452" | 2678 mm | 8' 9-7/16" |
| 9 | Tread 9 nose | 118-5/8" | 118.634" | 3013 mm | 9' 10-5/8" |
| 10 | Tread 10 nose | 131-13/16" | 131.816" | 3348 mm | 10' 11-13/16" |
| 11 | Tread 11 nose | 145" | 144.997" | 3683 mm | 12' 1" |
| 12 | Tread 12 nose | 158-3/16" | 158.179" | 4018 mm | 13' 2-3/16" |
| 13 | Tread 13 nose | 171-3/8" | 171.360" | 4353 mm | 14' 3-3/8" |
| 14 | Tread 14 nose | 184-9/16"− | 184.542" | 4687 mm | 15' 4-9/16" |
| 15 | Tread 15 nose | 197-3/4"− | 197.723" | 5022 mm | 16' 5-3/4" |
| 16 | Tread 16 nose | 210-7/8"+ | 210.905" | 5357 mm | 17' 6-7/8" |
| 17 | Tread 17 nose | 224-1/16"+ | 224.086" | 5692 mm | 18' 8-1/16" |
| 18 | Top plumb cut | 237-1/4"+ | 237.268" | 6027 mm | 19' 9-1/4" |
Step-off 13-3/16" (13.1816") · bottom cut 6-1/4" under 1" treads · last mark 19' 9-1/4" at the top plumb cut.
05 / Field guide
This sheet works a 138" floor-to-floor rise two ways. Option A uses the fewest risers the IRC allows, 18 at 7-11/16" on 10" treads. Option B adds one riser and uses 11" treads for a gentler 7-1/4" step. Both come with hook-once tape marks for the stringer edge, below the calculator.
138" ÷ 7.75 = 17.81, rounded up to 18 risers, each 7-11/16"− (7.6667", 194.7 mm). On 17 treads of 10" the stair lands 170" (14' 2") out from the upper floor edge and climbs at 37.5°; 2R + T scores 25.33".
Each step is 12-5/8"− along the stringer edge. Notches cut 6-1/16" deep, leaving 5-3/16" of throat in a 2x12; the cut length is 18' 2-1/4", so buy 20 ft stock.
One more riser drops each step to 7-1/4" (7.2632"). With 11" treads the run grows to 198" (16' 6"), 28" more than Option A, and the angle eases to 33.4° with 2R + T at 25.53".
The diagonal is 13-3/16", the throat 5-3/16", and the stringer cut length 20' 3/4" (over 20 ft).
Take the tread thickness off the bottom riser: 7-11/16" becomes 6-11/16" under 1" 5/4 or composite treads, 6-3/16" under 1-1/2" 2x6 treads and 6-5/8" under 1-1/16" oak treads. Every finished step then measures 7-11/16".
At the top, the last tread notch sits 8-11/16" below the finished floor for 1" treads. Seated on a 2x header, the header top goes 16-3/8" below the finished floor with oak treads.
18 risers means a handrail is required (four or more risers), 34" to 38" above the nosings.
The 170" run is more than the 6'-0" a cut stringer may span under DCA 6: set 2 4x4 support posts on 12" footings under the stringers, or build a landing.
138" is 6" under the 12'-0" point where DCA 6 requires a landing on deck stairs, and 13" under the 151" IRC limit for one flight.
The IRC wants 6'-8" measured plumb from the nosing line. With 12-1/2" of floor framing and ceiling, the opening above Option A must start 49-3/8" out from the bottom riser and run 120-5/8" (10' 5/8") to the top of the stair.
Floor to floor is the ceiling height plus the joists and subfloor: 138" is a 126" ceiling over 2x12 joists, or 128" over 2x10s.
Questions
18 risers at 7-11/16" with 17 treads, the fewest the IRC allows. For an easier climb, 19 risers at 7-1/4" with 18 treads.
About 18' 2-1/4" along the board for Option A, so 20 ft 2x12s; Option B needs 20' 3/4" (over 20 ft).
170" (14' 2") on 10" treads, or 198" (16' 6") on 11" treads with 19 risers. Leave a landing at least 36" deep beyond the last riser.
A 126" ceiling over 2x12 joists and a 3/4" subfloor, or 128" over 2x10s.
Not under AWC DCA 6, which asks for 2x12s. A 2x10 would keep only 3-3/16" of throat on Option A, under the 5" minimum.
Enter your exact rise in the calculator. 132" takes 18 risers and 144" takes 19; the riser count changes wherever the rise passes a multiple of 7-3/4".
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