Construction Calculators
Calculators

Construction Calculators

Free construction & DIY layout calculators with dimensioned diagrams and cut lists.

What you actually get

Most online calculators give you a single number. Here is a real, unedited result from the rafter calculator — a 24 ft span at a 6-in-12 pitch on 2x8 stock:

Dimensioned diagram — every cut labelled

Common rafter elevation with birdsmouth, ridge plumb cut and overhangScale elevation of one common rafter cut from 14 ft 5 9/16 in of stock. The board runs from the ridge board at the top left down to the tail at the bottom right over a horizontal run of 12 ft and a vertical rise of 6 ft, giving a line length to the ridge of 13 ft 5 in. The upper end is a plumb cut of 26.6 degrees against the ridge. At the wall plate a birdsmouth notch is cut with a 3 1/2 in seat and 6 3/8 in of heel height (HAP) remaining above the plate, using a seat cut of 63.4 degrees. Past the wall the tail projects 1 ft 1 7/16 in of sloped overhang and is finished with a plumb tail cut.Wall plateRidgeLine length to ridge — 13 ft 5 inCut length — 14 ft 5 9/16 inPlumb cut 26.6°at the ridgePlumb tail cutOverhang 1 ft 1 7/16 in(sloped)Run — 12 ftRise — 6 ftBirdsmouth — see detail below
Birdsmouth notch detail — seat depth and heel height (HAP)Enlarged detail of the birdsmouth where the rafter crosses the wall plate. The notch is an L-shaped cutout: a level seat 3 1/2 in deep bearing on the top of the plate, and a plumb heel cut at the outside face of the wall. Above the seat, 6 3/8 in of rafter material remains — this is the heel height, or HAP. The seat is sawn at 63.4 degrees and the heel at 26.6 degrees.Seat 3 1/2 inHeel height(HAP) 6 3/8 inSeat cut 63.4°level, bears on plateHeel cut 26.6°Birdsmouth detail (enlarged)

…plus the plumb and seat cut angles, the birdsmouth depth, the number of rafters and a printable cut list telling you how many boards to buy and how long to cut each one.

Try it with your own dimensions

What every calculator gives you

A dimensioned diagram

Every measurement labeled on a clear, print-friendly drawing. Readable in plain black and white, with no color-coding to squint at.

A printable cut list

Quantities and cut lengths laid out ready for the lumber yard.

Math you can check

Every result comes from standard geometry, with the formula and its source shown, so you can trust the number before you cut.

Built for your phone

Mobile-first and fast. No app to install, no sign-up, completely free.

How it works

  1. 1

    Enter your dimensions

    Span, pitch, wall length — whatever the calculator needs.

  2. 2

    Read the diagram and results

    The geometry and angles update as you type.

  3. 3

    Print or save the cut list

    Take it to the yard or the job site.

Which calculator do you need?

Not sure where to start? Pick by the job in front of you.

Framing or measuring a roof

Use the rafter calculator for common rafter length, the plumb and seat cut angles, and a full cut list from your span and pitch. To convert a roof’s rise and run into a pitch ratio, degrees, a percentage or a 1-in-N gradient, use the roof pitch calculator. Framing a hip roof instead of a gable? The hip roof calculator gives the hip rafter length, the jack rafter schedule and the double cheek cut angles for an equal-pitch hip.

Building a block wall

The cinder block calculator estimates how many blocks you need for a wall, the bags of mortar to lay them, and the concrete to fill the cores — with a dimensioned wall diagram and a course-by-course layout you can build from.

Frequently asked questions

Are these construction calculators free to use?
Yes. Every calculator is completely free, runs in your browser, and needs no sign-up and no app to install.
How accurate are the results?
Each result comes from standard geometry or published material coverage, and every page shows the formula and its source so you can check the number yourself. They are estimating tools, so always confirm critical dimensions and quantities against your actual materials and local building codes before you cut or buy.
Do the calculators work in feet-inches and metric?
Yes. On the calculators that use length units you can switch the display between imperial — feet, inches and fractions — and metric.
Can I print or save the cut list?
Yes. The dimensioned diagrams and cut lists are laid out to print cleanly in plain black and white, so you can take a paper copy to the lumber yard or the job site.
Do these replace an engineer or a building permit?
No. They help you plan a job and estimate materials, but they are not a substitute for a structural engineer, a licensed contractor, or your local permit and code requirements.

Live now: rafter, roof pitch, hip roof, cinder block and rebar calculators. Concrete, stairs and board feet are on the way.