Practical numbers, with the calculation methods visible
Carpentry Calcs is an independent collection of browser-based tools for people checking roof measurements, planning stair layouts and estimating materials. The site is maintained under the Carpentry Calcs name. It is not a building authority or an engineering design service.
Calculators run in your browser. Each tool page explains what its inputs mean, what the result includes and what you must check separately. Questions and corrections go directly to the site maintainer at fraunder@163.com.
Roof pitch and rafter length
For matching units, slope = rise ÷ horizontal run. Pitch in x:12 notation is slope × 12; percent is slope × 100; angle is arctan(slope) converted to degrees. The roof pitch calculator accepts all four input forms.
Theoretical rafter length is horizontal run × √(1 + slope²). The rafter calculator adds a horizontal overhang before applying that factor. Building-span mode assumes a centered ridge and divides span by two. It does not make ridge-board deductions or calculate birdsmouth depth.
Shed and lean-to roof heights
The shed roof calculator uses one full horizontal run. Rise is the difference between the two roof-edge heights, measured from the same level datum. A known pitch gives rise = run × pitch ÷ 12, and high-side height = low-side height + rise. Theoretical sloped length is √(run² + rise²). It does not convert these reference heights into post, wall or finished-building dimensions.
Stair layout
The stair calculator rounds total rise ÷ target riser height to choose a whole riser count. It divides total rise by that count to obtain equal risers, using the upper floor as the final tread. Tread count is one less than riser count; total run is tread count × entered tread depth.
Stair angle is arctan(actual riser height ÷ tread depth). Inclined stringer layout length is tread count × √(actual riser height² + tread depth²). This is the length over the repeated step layout, before end-cut and bearing allowances. A regression example is cross-checked against page 19 of the Johnson CALC-1500 instruction manual.
The tool's riser, tread and angle indicators are limited reference checks. They do not assess headroom, landings, handrails, loading, local rules or every detail of a finished staircase.
Baluster layout
The baluster spacing calculator uses the clear distance between post faces and the actual baluster width. With N balusters, there are N + 1 equal clear gaps. It finds the smallest nonnegative whole count that meets the entered maximum gap and lists centers measured from the left inside post face. The 156-inch worked example is checked against printed page 77 of the Calculated Industries Construction Master guide. This tool models level sections only and does not certify a guard or stair railing.
Solid-wood width change
The wood movement calculator uses equation 13–3 and the radial/tangential dimensional-change coefficients in Table 13–5 of the 2021 USDA Wood Handbook, Chapter 13. Estimated change is measured width × coefficient × change in wood moisture percentage points. All MC inputs are limited to the method's 6–14% range. Flatsawn and quartersawn selections approximate tangential and radial width movement respectively; they do not model mixed grain, engineered panels, warping or joint strength.
Precision and review
Calculations use unrounded values internally. Roof pitch, angle and percent display to two decimal places; the pitch chart displays factors to four. Stair angles display to one decimal place. Feet-and-inches lengths are rounded to the nearest 1/16 inch, and metric roof-length estimates to 0.001 m. Display precision does not improve the accuracy of the measurements you enter.
Baluster and wood movement lengths display inches to four decimals or millimeters to two. The baluster table also includes nearest-1/16-inch marks. Wood movement uses approximate material coefficients; the number of displayed digits is not a claim about material predictability.
Calculator changes are checked with automated tests and worked examples. The date on a guide reflects publication or an actual content update. A completed software check does not certify a construction design.
Help us correct a result
Send the tool URL, input values, units and the result you expected. An example with the same reference points is especially useful. See contact and corrections for the details to include.