| Scenario | Method | Inputs | Waste | Total | Rounded |
|---|---|---|---|---|---|
| Simple house | Rectangle | 40×30 ft, front+back+left+right, joints 8, overlap 0.5 | 10% | ~160.4 ft | 161 ft |
| Porch gap | Rectangle | 50×28 ft, all sides, exclusions 12 ft, joints 10 | 12% | ~179.8 ft | 180 ft |
| Complex roof | Custom runs | Runs: 18, 22, 16, 12 ft, joints 9, extra 6 ft | 15% | ~88.7 ft | 90 ft |
BaseAfterExclusions = max(0, Base − Exclusions)
JointAllowance = Joints × OverlapPerJoint
PreWaste = BaseAfterExclusions + JointAllowance + ExtraAllowance
Waste = PreWaste × (Waste% ÷ 100)
Total = PreWaste + Waste
RoundedTotal = ceil(Total ÷ Increment) × Increment
- Measure each roof edge that will receive gutters.
- Use Rectangle for simple buildings, or Custom runs for segmented edges.
- Enter Exclusions for edges without gutters, like open porch spans.
- Count Joints and set overlap per joint for splices.
- Choose a realistic Waste % for cuts, corners, and errors.
- Round up to match stocked section lengths and reduce shortages.
- Download CSV or PDF to share with your crew and supplier.
Roofline measurement planning
Accurate replacement length starts with clean field measurements. Record each fascia edge that will actually receive a gutter, not the full perimeter by default. Note short breaks at chimneys, valleys, or architectural returns. Use a consistent unit on site, then match that unit in the calculator so overlaps and rounding reflect what your supplier can deliver. Photograph tricky transitions and confirm access points for ladders, lifts, staging, and debris control in advance.
Segmented runs for complex elevations
Many structures include multiple roof planes and staggered edges. When a straight run is interrupted by a corner, step-out, or elevation change, treat it as separate runs. Enter each run length with the custom method to reduce guesswork and to plan miters, end caps, and hanger spacing per segment. This is especially useful on L-shapes and dormer-heavy layouts.
Joints, overlaps, and exclusions
Seams add length because sections overlap at each joint. A common splice overlap is about 0.5 ft (6 in) or 0.15 m, but manufacturer instructions, rivet patterns, and sealant details can change that value. Exclusions subtract length where gutters are not installed, such as open porch spans, scupper locations, or sections converted to internal drains.
Waste, rounding, and procurement
Waste covers trimming, damaged pieces, and layout adjustments at corners and returns. Typical waste ranges from 8–12% on straightforward lines and may increase on high-corner-count rooflines. Rounding up helps align the calculated total with stocked section increments and reduces the risk of shortages that can stall installation. Keep rounding modest to control overbuying.
Worked example data
Example (feet): Rectangle 50×28, all sides; exclusions 12; joints 10; overlap 0.5; waste 12%; rounding 1.
- Base = 2×(50+28) = 156 ft; BaseAfterExclusions = 144 ft
- JointAllowance = 10×0.5 = 5 ft; PreWaste = 149 ft
- Waste = 149×0.12 = 17.88 ft; Total = 166.88 ft; Rounded = 167 ft
Only measure edges that will receive gutters. Many buildings omit sections over patios, entry canopies, or areas draining to scuppers. Selecting only the needed sides improves ordering accuracy.
Use your intended section length to estimate seams per run, then add joints created by corners and transitions. When in doubt, round the joint count slightly up to cover field cuts and layout changes.
A common overlap is about 0.5 ft (6 in) or 0.15 m. Follow the gutter profile guidance and sealing method, because some systems need a longer lap for fasteners and sealant continuity.
Use 8–12% for simple layouts and increase it when there are many corners, short returns, or difficult access. If you are matching an existing profile, keep extra material for test-fitting.
Suppliers stock standard section lengths. Rounding up to the nearest increment helps your calculated total match what you can purchase, reducing the risk of being one short piece on installation day.
Use custom runs when the roofline is stepped, segmented, or not a simple rectangle. Entering each run prevents overestimating hidden edges and improves planning for corners, caps, and outlets.
Keep one unit per submission so overlaps and rounding stay consistent. If you need both, run the calculator twice or use the automatic secondary conversion shown in the results summary.