Understanding your result
The headline is the trim pieces in total, with the split by profile and the number of closures. The stats give the pieces, the closures, the tape rolls and the trim screws. The breakdown lists each edge with its length and its pieces, the closures for eave and ridge, the tape, the sealant and the screws.
The thing to check is the profile list: each line is a different part number at the supplier, in the panel colour, and a missing valley or sidewall line is a second delivery. The closures are the part most often left off a first order; they are matched to the panel profile, so order them with the panels.
The edges themselves come from the geometry group: ridge and hips from the hip rafter calculator, rakes from the rafter length calculator, eaves from the plan. The panels and their screws are counted by the panel calculator and the screws calculator.
How we calculate this
Every profile is counted the same way, by effective length, and the only judgement is the lap: 6 inches is right for ridge cap and valleys, where water runs along the joint, and generous for eave and rake trim, which can lap 2 to 4 inches. The closures are counted per panel width rather than per foot because they are made in panel-wide pieces (36 inches for a 36-inch panel) matched to the rib pattern.
The tape and sealant allowances are the industry’s rules of thumb rather than a measurement, which is why both are rounded up and shown as separate lines you can edit after the first roof. The guide to metal roof panel maths shows the trim in installation order, and the flashing and drip edge guide covers the wall and valley details that the trim must match.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Stick length | 10 ft | Standard length of metal roof trim; 12 ft available |
| Overlap | 6 in | Manufacturers’ details for ridge cap and valley (6 in); eave and rake 2 to 4 in |
| Waste | 5% | Estimating practice for mitres and end cuts |
| Closure strips | one per panel width at the eave and on each side of the ridge | Manufacturers’ installation guides |
| Butyl tape roll | 45 ft | Common roll length of ¾-in butyl tape (also 30 and 50 ft) |
| Sealant | 1 tube per 20 ft of ridge, valley and wall flashing | Estimating practice |
| Trim screws | 1.5 per foot | Manufacturers’ guides: screws at 12 in along trim, closer at ends |
Assumptions last reviewed October 7, 2026.
The calculator does not count pipe boots, vents, snow guards, gutter apron or the transition trim between two pitches, and it uses one lap and one stick length for every profile. The drip edge calculator is the shingle-roof version of the eave and rake lines and uses the same arithmetic, and the standard sizes table lists the stick lengths and panel widths in one place.
Two worked examples
A gable roof with 10-foot sticks
Ridge 40 feet, eaves 80 feet, rakes 72 feet, no valleys or walls, 10-foot sticks lapped 6 inches, 36-inch panels, 5% waste.
- Effective stick: 10 ft − 6 in = 9.5 ft
- Ridge cap: 42 ÷ 9.5 = 4.4, so 5; eave trim: 84 ÷ 9.5 = 8.8, so 9; rake trim: 75.6 ÷ 9.5 = 8
- Trim: 22 pieces
- Closures: 80 ft ÷ 3 ft = 27 outside; 2 × 40 ft ÷ 3 ft = 27 inside
- Tape: (80 + 80 + 72) × 1.1 = 255 ft, 6 rolls; sealant 2 tubes; trim screws about 300
Twenty-two sticks in three profiles, 54 closures, six rolls of tape: the trim order for the same roof the panel calculator counted at 29 panels.
A hip roof with a valley and a sidewall, 12-foot sticks
Ridge and hips 90 feet, eaves 140 feet, no rakes, 30 feet of valley, 24 feet of sidewall, 12-foot sticks lapped 4 inches.
- Effective stick: 12 ft − 4 in = 11.67 ft
- Ridge and hip cap: 94.5 ÷ 11.67 = 8.1, so 9; eave trim: 147 ÷ 11.67 = 12.6, so 13; valley: 3; sidewall: 3
- Trim: 28 pieces
- Closures: 47 outside, 60 inside (every hip and ridge foot takes closures both sides)
- Tape: 444 ft, 10 rolls; sealant 8 tubes; trim screws about 450
The hips triple the ridge line, and with it the inside closures and the tape; on a hip roof the ridge and hip cap is the biggest trim line.
Where to find your inputs
Ridge length. The ridge plus every hip, measured along the slope for hips (the hip rafter calculator), plus dormer ridges.
Eaves and rakes. From the plan: the eaves are the horizontal edges, the rakes the sloped gable edges (half the width times the pitch factor, each).
Valleys and walls. Valley lengths along the valley line; sidewall where the roof runs along a wall; endwall where the top of a slope meets a wall.
Coverage width. The panel’s coverage, for the closures; 36 inches for standard ribbed panels, 24 for corrugated, the seam spacing for standing seam.
Common mistakes
- Dividing by the stick length. The lap costs 5 percent on ridge cap and the mitres cost more. Use the effective length.
- No closures. Without outside closures at the eave the roof whistles and lets wasps in; without inside closures at the ridge, rain blows under the cap.
- Rake trim under the panel. Rake goes over; eave goes under. The flashing guide shows the order.
- Hip cap counted as ridge cap. Same profile on many panels, but hips also need a peak cap where they meet the ridge, and closures on both sides of every hip.
- One colour for the trim, another for the panels. Order the trim from the panel’s colour chart in the same batch.
- Forgetting the tape. Butyl tape under the ridge cap and the laps is what makes an exposed-fastener roof tight; sealant from a tube is not a substitute along a lap.
Questions people ask
- What trim does a metal roof need?
- Ridge cap (and hip cap on a hip roof) over the top; eave trim, which is the drip edge, under the panel at the bottom; rake or gable trim over the panel edge at the gable ends; valley trim in any valley; sidewall and endwall flashing where the roof meets a wall; and closure strips shaped to the panel profile under the panel at the eave and over it at the ridge. Pipe boots and vents are extra.
- How many pieces of ridge cap do I need?
- Divide the ridge and hip length by the effective length of a stick, which is its length less the overlap: 9.5 feet for a 10-foot stick lapped 6 inches, then add about 5 percent for cuts. A 40-foot ridge is 42 feet with waste, 4.4 effective sticks, so 5 pieces. A hip roof adds each hip to the length and needs a cap at each peak.
- What are closure strips?
- Foam (or formed metal) strips cut to the panel's profile that fill the gaps under the ribs. Outside closures go under the panel at the eave, with the panel's profile on top, to keep wind, rain and insects out; inside closures go on top of the panel under the ridge cap, with the profile below. One per panel width at the eave and one per panel on each side of the ridge: 27 outside and 27 inside on the calculator's default roof. Vented ridge closures provide attic ventilation.
- How much overlap for metal trim?
- Ridge cap and valley trim lap at least 6 inches; eave and rake trim 2 to 4 inches; all laps face away from the prevailing wind and downhill on a slope. The calculator uses one lap figure for all the trim; enter 6 inches for a conservative count or run the eave and rake separately with 3 inches.
- Where does the butyl tape go?
- Under the ridge cap on both sides, along the side laps of the panels, under the eave trim where it meets the panel, and under sidewall and endwall flashing. The calculator allows the ridge twice, the eaves, rakes and walls once and the valleys twice, with 10 percent extra, in 45-foot rolls; sealant tubes cover the ends and corners.
- Does rake trim go over or under the panel?
- Over. Rake (gable) trim covers the cut or hemmed edge of the end panel and is screwed down through the panel into the rake board, with tape under it. Eave trim is the opposite: under the panel, so water running off the panel drops onto it. Mixing them up is the commonest trim mistake on a first metal roof.