How do I calculate the number of stairs I need?

Divide the total rise by the maximum riser height and round up. For a 108 inch rise with a 7.75 inch limit, that is 14 risers of about 7.71 inches each.

How do I calculate stair stringer length?

Work out the total run, then take the square root of the rise squared plus the run squared. For a 108 inch rise and a 130 inch run, the stringer is about 169 inches.

What is the standard rise and run for stairs?

The International Residential Code allows risers up to 7 3/4 inches and requires treads of at least 10 inches for homes. Local codes can be stricter, so check before building.

Stair calculator

Rise, run and stringer from one measurement

Measure floor to floor. This divides the height into equal steps, keeps each riser under your limit, and gives the run and the stringer length to cut.

Total rise, finished floor to finished floor

Maximum riser height

Tread depth (run)

Top of the stair

Top tread is the upper floorTop tread is one step down

Defaults are the common residential limits in the International Residential Code: risers up to 7¾ in and treads at least 10 in. Your local code may differ and always wins. Nothing you enter is saved or sent.

0risers

each riser

treads

total run

stringer length

stair angle

riser + tread

The method

Divide the total rise by the tallest riser you are allowed, and round up: that is the number of risers. Divide the total rise by that number for the exact height of each one. Every riser must be the same; an odd step is the one people trip on.

Worked example. Floor to floor is 108 in. 108 ÷ 7.75 = 13.9, so 14 risers. Each riser: 108 ÷ 14 = 7.71 in, a little under 7 3/4. With the upper floor as the top tread there are 13 treads; at 10 in each the total run is 130 in, or 10 ft 10 in. The stringer runs about 169 in, just over 14 ft.

Treads and risers

There is always one fewer tread than risers when the upper floor acts as the last step. If the stair finishes one step below the floor, with a full tread at the top, the counts are equal and the run is one tread longer.

Comfort check

Stairbuilders use a rule of thumb: riser plus tread should come to roughly 17 to 18 inches. A 7.7 in riser with a 10 in tread gives 17.7, which is comfortable. Shallow treads with tall risers feel steep; deep treads with short risers make you shuffle.

Before you cut

Measure finished to finished. Include flooring that is not down yet, at both the top and the bottom.
Check headroom. Codes also set a minimum clear height above the stair.
Allow for tread thickness when laying out the stringer: the first riser is cut shorter by one tread thickness.
Confirm the code. Riser, tread, width, landing and handrail rules vary by place and by building type.

The quantity is sorted. Now price the job.

ScopeBid: Estimate & Invoice is an offline estimate and invoice app for independent service professionals, on iPhone and iPad. Its listing says Profit Guard shows gross margin and markup side by side before a quote is sent, and each quote goes out as a PDF.

Get ScopeBid on the App Store

Your first three quotes are free with full PDFs. ScopeBid Pro is an optional auto-renewing subscription for unlimited quoting and the wider job-costing and invoicing workflow. Check the App Store for current terms.

Honest Little Apps publishes both ScopeBid and this page. This is a separate browser tool and does not sync with the app. App details checked November 10, 2026.

On a computer? Open it on your iPhone

Point your iPhone camera at the code, then tap the link.

QR code for ScopeBid: Estimate & Invoice on the App Store

Open ScopeBid on the App Store

ScopeBid screenshot showing a customer price with estimated cost and gross profit before sending a quote — From ScopeBid's App Store listing.