RafterCAD

Language

Live calculations Nearest 1/16″

Job name & address Optional

Job name

Job address

Cut sheet date: · automatic

Roof Type

Roof Style

Roof Span / Building Width

Field measure outside of wall to outside of wall, including sheathing if applicable.

Rafter Span - Horizontal Distance

Outside wall to ridge centerline, before the ridge deduction. Overhang is entered later.

Calculate Rafter Using:

Pitch for this rafter

/ 12

Enter the rise only: 6 for a 6:12 roof.

Lumber Type

Ridge Size

Actual thickness, not nominal size.

Rafter size

Choose a rafter size.

Subfascia size

Choose a subfascia size.

Horizontal birdsmouth seat

Enter your actual wall thickness.

Wall thickness

Custom stock dimensions

Rafter depth · inches

Subfascia depth · inches

Actual subfascia thickness · inches

Standard 2× subfascia is 1½″ thick. Choose Custom depth to enter a different thickness.

Choose “Custom depth” to enter actual stock dimensions.

Rafter Tail

Horizontal
Overhang

Overhang
Measured To

Enter inches or feet and inches, for example 16 or 1′ 4″.

Tail cut

Plumb face with a level bottom clip to suit the subfascia.

Tail clearance Optional

Bottom clearance · in

Clearance is measured along the tail cut face.

Verify the structural design and test one pattern rafter before bulk cutting. Read the use & liability notice.

Your job and measurements are saved on this device and restored when you reopen the app.

Measurement help

Building width

Building width is the horizontal distance between the outside faces of the opposing walls. The outside-wall reference corresponds to the actual wall thickness entered for the birdsmouth seat. Do not measure between the inside wall faces; exclude the overhang.

Rafter span

Rafter span is measured horizontally from the outside face of the supporting wall to the ridge centerline, before the ridge deduction. The outside-wall reference corresponds to the actual wall thickness entered for the birdsmouth seat. Exclude the overhang; do not enter the sloping rafter length.

Overhang

Overhang is measured horizontally outward from the outside face of the supporting wall to the selected endpoint. The outside-wall reference corresponds to the actual wall thickness entered for the birdsmouth seat. Do not measure from the inside wall face or along the roof slope.

Feet, inches & fractions

The span has separate feet and inches boxes. Other measurements accept inches (7.25), fractions (7 1/4), or feet and inches (1' 4"). Bare numbers are inches.

Try a reference example

Load a complete setup from the checked drawings.

Earlier rafter-face examples

These use overhang measured to the rafter face.

Your cut sheet starts here

Enter your roof, lumber and tail dimensions to create the drawing and cut sheet.

MeasureInputCutBuildOn-site

Rafter cut sheet

Cut sheet date

Check your measurements

Review these entries before exporting or cutting.

Export your cut sheet, then choose Share PDF or Save PDF.

Dimension units

Feet & inches · nearest 1/16″

Applies to measurements, drawings and printed sheets.

Input checks

Inputs used for this cut sheet

Disclaimer of Professional Services & Limitation of Liability

Purpose and limitations. RafterCAD, provided by Belleson Group LLC ("RafterCAD") is a calculation and layout aid for rafter geometry. It does not provide architectural or engineering services, structural design, construction supervision, or approval for construction. Calculated dimensions, diagrams, and input checks do not establish structural adequacy or compliance with applicable codes, regulations, permits, or approved plans.

Structural members and connections. Belleson Group LLC recommends that all structural members, bearing conditions, and connections be sized, designed, and reviewed by a qualified design professional appropriately licensed in the project jurisdiction. RafterCAD does not determine allowable loads, spans, member sizes, notch limits, fastener requirements, or connection capacity. Obtain any professional services and approvals required for the project before construction.

Verification and pattern rafter. Before cutting or installation, independently verify all inputs, units, reference points, calculated dimensions, material dimensions, and actual field conditions against the approved plans. Cut and test-fit one pattern rafter before bulk cutting. Confirm ridge or ledger fit, birdsmouth bearing, tail geometry, and subfascia clearance. Resolve discrepancies before proceeding.

Construction responsibility. The user and the parties responsible for construction retain responsibility for construction means, methods, techniques, sequences, procedures, temporary support, bracing, installation, and site safety. RafterCAD does not direct, supervise, or control construction activities.

Warranties and liability. To the fullest extent permitted by applicable law, RafterCAD is provided "as is" and "as available," without express or implied warranties, including warranties of accuracy, completeness, merchantability, or fitness for a particular purpose. To the same extent, Belleson Group LLC and its owners, officers, employees, agents, and representatives disclaim liability for losses, damages, costs, or claims arising from use of or reliance on RafterCAD, including those relating to structural member sizing, bearing, connections, fabrication, installation, or construction means and methods.

Rights preserved. Nothing in this notice excludes or limits liability that cannot lawfully be excluded or limited, or restricts any nonwaivable statutory right.

RafterCAD · Rafter Layout & cut detailsReal-Time Cut Sheets

Rafter Layout

SIDE VIEW

Rafter DimensionsTap Enlarge for full dimensionsSchematic · dimensions govern

Cut details

Cut and test-fit one pattern rafter before bulk cutting. Dimensions govern; drawings are schematic. Refer to the summary page for inputs and the use & liability notice.

RafterCAD · Building & Roof CheckReal-Time Cut Sheets

Building & Roof Check

Entered side

Measurement guide & reference points

A · Full rafter: Along the top edge, from the ridge or upper-beam plumb cut to the tail.
B · Ridge / upper cut to wall: Along the top edge to directly above the outside wall line.
C · Tail cut face: Plumb tail: vertical face at the back of subfascia. Square tail: the face perpendicular to the rafter top, sized to the angled subfascia, with a matching-depth underside parallel to the rafter top.
D · Ridge / upper support height: Vertically from the low-wall plate top to the rafter top at the ridge or upper-beam face.
E · Height above plate: Vertically from plate top to rafter top at the outside wall line.

The seat extends inward from the outside wall line. Choose a plumb face with a level bottom clip, or a square cut perpendicular to the rafter top. Square tails use an angled subfascia. The entire exposed tail is trimmed to a constant depth, with its underside parallel to the top edge from the end face back to the outside wall line. The trim stops at the wall; the inboard stock and birdsmouth seat remain at their specified dimensions. C is subfascia depth less clearance, capped at stock depth. When overhang includes the subfascia, its thickness is deducted along the rafter slope. Gable roofs default to a centered ridge. For unequal opposing pitches or an offset ridge, enter this side’s horizontal rafter span to the ridge centerline and use this side’s pitch. Calculate the opposite side separately and verify the common ridge elevation. Shed roofs default to the full building width minus the full upper-beam thickness. Both layouts assume a plumb upper cut with the beam top flush to the rafter top at its face. Shed mode includes the low-wall birdsmouth and tail; a high-end birdsmouth or additional high-end overhang is not included.

When measuring overhang to the outside of subfascia, its thickness is deducted from the tail run. Its top meets the roof plane at its outside edge. Bottom clearance reduces C.

Calculation formulas

Height mode solves D = (R − s)m + d√(1 + m²), where D is entered ridge-top height, R is horizontal run after the ridge or ledger deduction, s is seat width, d is actual rafter depth and m is pitch / 12. The tail and subfascia do not change the solved pitch. Calculations use full precision; the pitch shown is rounded to four decimal places.

Pitch is displayed as rise per 12 inches to the nearest 1/16 inch and as a decimal; cuts use full precision.

m = pitch / 12 · q = √(1 + m²) · Automatic rafter span = building width / 2 for gable, or the full building width for shed. Enter a custom rafter span for this side when needed. R = rafter span − half the ridge thickness (gable), or rafter span − full ledger thickness (shed) · d = rafter depth · s = seat width · t = subfascia thickness in outside-face mode (otherwise 0).

A = (R + overhang − t)q
B = Rq
Plumb: C = min(subfascia depth + tm − clearance, dq). Square: C = min(subfascia depth − clearance, d). For square tails, t = actual subfascia thickness / q in outside-face mode.
E = dq − sm
D = Rm + E

Notch depth perpendicular to stock = sm / q. Plumb bottom clip run = min((dq − C) / m, tail run). The clip may terminate at the outside wall face, but must not cut above the birdsmouth seat. Square-tail underside = top-edge line + Cq vertically. Depth removed perpendicular to the top = d − C. The square end face extends Cm/q inward and C/q downward from its top long point. Full precision is used internally; displayed lengths round to 1/16″.

Verify member sizing, bearing and notch limits for your project. Cut and check one pattern rafter before repeating.

Reference checks

Checked against the supplied PDF and screenshots. The gable drawing examples use 24′ span, 12:12 pitch and 11¼″ stock. The supplied shed ledger drawing uses a 12′ span and the full 1¾″ ledger deduction. The shed arithmetic example uses 10′ span, 9:12 pitch and 7¼″ stock. Some source labels round to ⅛″; the app displays 1/16″. Each difference is shown in the tables.