Build cleaner roof layouts with instant rafter measurements. Test pitch, overhang, spacing, and totals confidently. Get practical outputs for planning cuts before site work.
| Case | Run | Pitch | Overhang | Roof Length | Spacing | Approx. Total Rafter |
|---|---|---|---|---|---|---|
| Shed Roof A | 12 ft | 4 in 12 | 1.5 ft | 24 ft | 2 ft | 14.23 ft |
| Porch Roof B | 3.6 m | 18° | 0.45 m | 7.2 m | 0.6 m | 4.26 m |
| Lean-To Roof C | 10 ft | 6 in 12 | 1 ft | 20 ft | 16 in | 12.30 ft |
These examples are sample planning values. Actual cuts may change with fascia detail, birdsmouth layout, and structural design.
This calculator gives fast layout values. It does not replace engineering checks, structural sizing, fastening design, or local building code review.
A mono pitch roof uses one simple slope. It is common on sheds, porches, lean-to roofs, and modern extensions. Even with a simple shape, framing errors can waste time and material. Builders often need fast checks before cutting timber. This calculator helps by turning the main roof dimensions into useful layout numbers. You can estimate rise, slope, rafter length, roof area, and total material in one place. That makes early planning cleaner and easier.
The vertical rise shows how much height the roof gains from the low side to the high side. The main rafter length gives the sloped framing length across the run only. The tail length adds the overhang portion. When those two values are combined, you get the total rafter cut length before fine trimming. The slope factor is also helpful. It lets you convert flat dimensions into sloped dimensions quickly. Roof area is useful for estimating sheathing, metal panels, membranes, or underlayment.
Rafter spacing changes the number of pieces required. A small spacing usually means more rafters and greater lumber use. Wider spacing reduces count, but structural rules still apply. Waste percentage helps with ordering. Real jobs include trimming, offcuts, small mistakes, and irregular ends. Adding a modest waste allowance can prevent shortages. This is especially useful when roofing sheets or boards come in fixed lengths.
This tool is best for planning and estimating. It gives quick values that support sketches, quotes, and material lists. It also helps compare pitch options before construction starts. Still, final cuts should always be checked against actual wall heights, birdsmouth details, fascia depth, insulation buildup, and local code. Timber size, loading, wind, and fastening design must also be reviewed. Use the calculator to work faster, then verify every field dimension before installation.
It is a roof with one continuous slope. People also call it a shed roof or lean-to roof in many projects.
Horizontal run is the flat distance from the high wall line to the low wall line. It is not the sloped rafter length.
Yes. The calculator accepts pitch in degrees or as rise per 12. It converts both methods into the same roof angle.
Yes. Overhang adds a tail section beyond the main run. That extra section increases the final rafter length and roof area.
Roof area helps estimate coverings and sheet goods. It is useful for metal roofing, decking, membranes, underlayment, and sheathing orders.
No. It calculates geometry and planning values. Structural member sizing still depends on loads, span rules, grade, species, and code.
The count method includes both ends of the roof line. That gives a practical estimate for evenly spaced rafters across the full length.
Use it for planning first. Then verify wall heights, seat cuts, fascia detail, and actual site dimensions before making final cuts.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.