Craft Quantities
Plan & Takeoffs

Renovation & Construction

Stair Stringer Drop Cut Calculator

How much to take off the bottom of a cut stringer so the first step finishes level with all the others once the treads and the floor finishes are on.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
From the surface the stringer will stand on, up to the bare landing deck.

Take the measurement on what is actually there today — subfloor to structural landing — and let the two build-up fields below account for the finishes that arrive later. Measuring to a finish that has not been laid is guesswork dressed up as a dimension.

The number of risers the flight will have, floor to floor.

One more than the number of treads, because the top riser lands on the floor above rather than on a tread. Divide the finished rise by this to get the height every riser has to hit.

The thickness of the treads that will sit on the stringer cuts.

Use the finished assembly, not the substrate: a plywood tread with a hardwood cap on top is the sum of the two, and a carpet pad adds to it again. This is the single measurement the drop cut exists to absorb.

The bottom tread's thickness, where it differs from the rest.

Feature starter steps are often built heavier than the treads above them, and a bullnosed starter on a hardwood stair can be twice the thickness. Where the bottom tread matches the others, enter the same figure and the flight comes out uniform.

Finish going down at the base of the stair after the stringer is set.

Tile on a bed, engineered board on an underlay, a levelling screed — whatever will be added under the bottom step once the stair is in. It reduces the drop cut directly, and forgetting it is why so many bottom steps end up short.

Finish going down on the landing above after the stringer is set.

The landing finish raises the top walking surface and so raises the total rise the flight has to climb. It does not change the drop cut, but it does change the height every riser has to be, which is why it belongs in the layout rather than in the fixing.

Drop cut at the base of the stringer

0.5 in

High confidence

Take 0.50 in off the bottom horizontal cut, keeping the cut square and the bearing full. The tread arrangement entered introduces 0.00 in of variation across the flight, inside the 3/8 in the model codes allow.

Uniform riser height for the finished flight
7.13 in
Total finished rise
9.5 ft
First riser as built
7.13 in
Second riser as built
7.13 in
Top riser as built
7.13 in
Variation this introduces across the flight
0 in
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • Derived geometry, and a standard carpentry layout rule rather than a code provision: the stringer's first riser is cut short by the thickness of the tread that will sit on it, less any floor finish that goes down after the stair is set
  • IRC R311.7.5.1 and IBC 1011.5.4 set the tolerance the result is judged against — no more than 3/8 in (9.5 mm) between the greatest and smallest riser in a flight

Inputs used

Rise Measured to the Bare Deck
9.5 ft
Risers in the Flight
16
Finished Tread Thickness
1 in
Starter Tread Thickness
1 in
Lower Floor Build-Up
0.5 in
Upper Landing Build-Up
0.5 in

Intermediate steps

Uniform riser height for the finished flight
7.13 in
Total finished rise
9.5 ft
First riser as built
7.13 in
Second riser as built
7.13 in
Top riser as built
7.13 in
Variation this introduces across the flight
0 in
Final result0.5 in

Confidence note: Take 0.50 in off the bottom horizontal cut, keeping the cut square and the bearing full. The tread arrangement entered introduces 0.00 in of variation across the flight, inside the 3/8 in the model codes allow.

What this calculation does not cover

  • Cut stringers carried on their horizontal cuts. Housed stringers with wedged treads set the tread position from the housing instead, and the adjustment is made in the routing rather than at the base.
  • Assumes the stringer's top cut is set from the bare landing deck. Where the stair hangs from a header at a fixed height instead, the top attachment absorbs part of this and has to be set out separately.

Add the equipment this sizes

This result is a specification — 0.5 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

9.5 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations2
  1. Derived geometry, and a standard carpentry layout rule rather than a code provision: the stringer's first riser is cut short by the thickness of the tread that will sit on it, less any floor finish that goes down after the stair is set
  2. IRC R311.7.5.1 and IBC 1011.5.4 set the tolerance the result is judged against — no more than 3/8 in (9.5 mm) between the greatest and smallest riser in a flight

Which documents these citations point at

  • International Residential Code — R311.7.5.1 (United States)One- and two-family dwellings and townhouses up to three storeys — structure, fire safety, energy, plumbing, mechanical and electrical in a single document.
  • International Building Code — 1011.5.4 (United States)Buildings other than the dwellings the IRC covers — occupancy, egress, fire resistance and structural provisions.

A code or standard has force only where a jurisdiction has adopted it, usually with local amendments. This site holds no adoption data for any authority, so check what is in force with the authority where you build. Any section cited above without an edition should be checked against the edition in force where you build. What it would take to know.

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Called something else where you work? Stair rise and going — the term in each market, how close the equivalence really is, and the standard that governs it.

How to calculate stair stringer drop cut in 7 steps

  1. Rise Measured to the Bare DeckFrom the surface the stringer will stand on, up to the bare landing deck.
  2. Risers in the FlightThe number of risers the flight will have, floor to floor.
  3. Finished Tread ThicknessThe thickness of the treads that will sit on the stringer cuts.
  4. Starter Tread ThicknessThe bottom tread's thickness, where it differs from the rest.
  5. Lower Floor Build-UpFinish going down at the base of the stair after the stringer is set.
  6. Upper Landing Build-UpFinish going down on the landing above after the stringer is set.
  7. Drop cut at the base of the stringerThe tool computes the drop cut at the base of the stringer from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Why does the bottom riser need cutting shorter at all?
Because every step in the flight except the first gets a tread both above and below it, so the tread thicknesses cancel out. The bottom step has a tread on top and the floor underneath, so its riser is taller than the layout by exactly the thickness of that tread — and the cure is to take the same amount off the foot of the stringer before it is fixed.
What happens if I drop the stringer and then the floor finish goes down anyway?
The bottom riser ends up short by the thickness of that finish, and if it is a tiled floor on a bed the shortfall will exceed the tolerance on its own. This is the commonest single-step failure on an inspection, and it is why the drop cut is the tread thickness less the finish rather than the tread thickness alone.
My starter tread is thicker than the rest. Where does the difference go?
It moves into the second riser and out of the top one, because the whole cut pattern above the first step shifts by the difference. A 50 mm starter under 28 mm treads throws 22 mm into two risers, which is more than twice the variation the codes allow, so the extra thickness has to be absorbed by re-cutting the stringer rather than by hoping nobody measures.
Should I measure the total rise before or after the finishes?
Measure what exists, then add what is coming. Subfloor to bare landing deck is a real dimension you can put a tape on; finished floor to finished landing is a prediction. Entering the measurement with the two build-ups separately means the layout follows the finishes even when they change late, which they routinely do.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.