How many metal roof panels for a 12×20 roof?

Data checked October 2026

Short answer

A 12×20 ft gable roof at 4/12 with 6-in overhangs needs 14 panels of 36-in coverage (7 per side), each 6' 11" long, plus about 231 screws.

Panels per side: 21 ft along the eave (overhangs included) ÷ 3 ft of coverage = 7, rounded up to 7.
Panel length: 6.5 ft of run per side × 1.054 (4/12 multiplier) = 6' 11", to the next inch.
From store stock, the cheapest route is 7 × 14-ft panels ($55.99 each) cut in half — two 6' 11" pieces per panel, factory end at the eave and the cut end under the ridge cap: $392 versus about $392 cut to length.
Trim: 3 ridge caps (10½ ft, lapped to 10), 5 pieces of eave trim, 3 of rake trim, and 28 foam closure strips for the eaves and ridge.
In 5V crimp (24-in coverage) the same roof takes 22 panels — 8 more to haul and screw, about $517 in panels.
Weight: about 201 lb of 29-ga panels — roughly 70 lb per square, versus about 220 lb per square for architectural shingles.
12×20 is a common lean-to and carport size; switch the calculator to single slope if it has one.

Adjust it to your exact job

Building

Roof shape

Lengthalong the eave

= 20' · 6.1 m

Widtheave to eave

= 12' · 3.66 m

Pitch

Exact pitch

/12

Multiplier 1.054

Eave overhang

= 6"

Gable overhang

= 6"

Panels

Profile

Panel lengths

Solid deck with underlayment

Turn off for panels screwed straight to purlins (pole barns, open sheds).

Panels to order

7× 14 ft

14-ft stock panels — cut each into two 6' 11" pieces for 14 roof panels · 7 per side × 2 sides · 36-in coverage · 97 lin ft of panel

Roof area: 288sq ft2.9 squares
Screws: 23180 per square, panels only
Panel run (cut): 6' 11"eave edge to ridge, along the slope
Panel weight: 201lb29 ga at 0.70 lb/sq ft

Trim & closures

Trim pieces and closure strips
Item	Length	Buy
Ridge cap	21 ft	3 × 10½ ft
Eave trim	42 ft	5 × 10½ ft
Rake trim	28 ft	3 × 10½ ft
Inside closures (eave)	42 ft	14 × 36 in
Outside closures (ridge)	42 ft	14 × 36 in

Compare panel profiles

Panels by profile
Profile	Panels	Lin ft	Panel cost
36-in rib panel36-in coverage	14	97	$392
5V crimp24-in coverage	22	152	$517

Screw pattern

Fabral calls for 80 screws per square on exposed-fastener rib panels: screws at the eaves, ridge and end laps, and at every intermediate support. Drive them snug — an over-tightened washer leaks as surely as a loose one. Trim and side-lap stitch screws come on top of this count.

Shopping list

7 panels 36-in rib panel panels, 14 ft stockcut each into two 6' 11" pieces · 7 per side at 36-in coverage · 97 lin ft$392
231 screws #14 × 1 in Woodtite roofing screws (OSB/plywood deck)80 per square; use #10 × 1½ in into purlins
3 pieces Ridge cap, 10½ ft × 14 in21 ft, lapped 6 in$111
5 pieces Eave trim / drip edge, 10½ ft42 ft
3 pieces Rake (gable) trim, 10½ ft28 ft
14 strips Inside foam closure, 36 in (eaves)$39.06
14 strips Outside foam closure, 36 in (ridge)$39.06
1 rolls Synthetic underlayment, 10-sq roll (42 in × 286 ft)$130
1 buckets 1-in plastic cap nails, bucket of 3,000$45.49

Estimated total$757

Cost estimate

Tap a price to use your store's

36-in rib panel panel, 14 ft (29 ga)
7 panels × $
$392
Ridge cap, 10½ ft
3 pieces × $
$111
Foam closure strips, 36 in
28 strips × $
$78.12
Synthetic underlayment, 10-sq roll (42 in × 286 ft)
1 rolls × $
$130
Plastic cap nails (3,000)
1 buckets × $
$45.49

Materials total$757

29 ga Galvalume prices from McCoy's (San Marcos, TX), Oct 23, 2026; cut-to-length uses the same per-foot rate. Eave and rake trim vary by supplier — get a quote with the panels.

Did this answer your question?

Compare

The same 12×20 roof at other pitches

Pitch	Panel length	Panels	Roof sq ft	Screws	Panel cost
3/12	6' 9"	14	281	226	$392
4/12	6' 11"	14	288	231	$392
5/12	7' 1"	14	296	237	$427
6/12	7' 4"	14	305	245	$427
8/12	7' 10"	14	328	263	$427

How this was worked out

Roof area: 21 × 13 ft of plan × 1.054 = 288 sq ft (2.9 squares). At Fabral's 80 screws per square that's 231 panel screws — #14 × 1 in Woodtite into a plywood or OSB deck, #10 × 1½ in into purlins — before trim and stitch screws.

Under 3/12 the IRC requires lap sealant on exposed-fastener panels; 36-in rib panels are rated down to 2½/12 by their makers and 5V crimp to 3/12. At 4/12 either profile is fine without sealant.

The full method, material data and tips are on the main metal roofing calculator page.

Similar jobs

Other sizes people check

Sources

Data behind this answer

Fabral Grandrib 3 product specification — 36-in coverage, 2½:12 minimum, 80 screws per square; cut to length up to 40 ft · checked October 2026
Best Buy Metals Tuff-Rib and 5V crimp — 36-in coverage cut to the inch 3–45 ft; 29 ga 0.70 lb/sq ft; 5V 24-in coverage, 3:12 minimum · checked October 2026
McCoy's metal roofing (Metal Sales StrongPanel, 5V, ridge cap, closures) — 8–20 ft panel prices, 10½-ft ridge cap $36.99, closure strips $2.19–2.79 — 2026-10-23 · checked October 2026
2024 International Residential Code R905.10 (UpCodes) — lapped metal panels 3:12 minimum (½:12 with lap sealant; standing seam ¼:12) · checked October 2026
Owens Corning ProArmor synthetic underlayment — 929 sq ft net per roll with 3-in laps · checked October 2026

Short answer

A 12×20 ft gable roof at 4/12 with 6-in overhangs needs 14 panels of 36-in coverage (7 per side), each 6' 11" long, plus about 231 screws.

Panels per side: 21 ft along the eave (overhangs included) ÷ 3 ft of coverage = 7, rounded up to 7.

Panel length: 6.5 ft of run per side × 1.054 (4/12 multiplier) = 6' 11", to the next inch.

From store stock, the cheapest route is 7 × 14-ft panels ($55.99 each) cut in half — two 6' 11" pieces per panel, factory end at the eave and the cut end under the ridge cap: $392 versus about $392 cut to length.

Trim: 3 ridge caps (10½ ft, lapped to 10), 5 pieces of eave trim, 3 of rake trim, and 28 foam closure strips for the eaves and ridge.

In 5V crimp (24-in coverage) the same roof takes 22 panels — 8 more to haul and screw, about $517 in panels.

Weight: about 201 lb of 29-ga panels — roughly 70 lb per square, versus about 220 lb per square for architectural shingles.

12×20 is a common lean-to and carport size; switch the calculator to single slope if it has one.

Adjust it to your exact job

Building

Roof shape

Lengthalong the eave

= 20' · 6.1 m

Widtheave to eave

= 12' · 3.66 m

Pitch

Exact pitch

/12

Multiplier 1.054

Eave overhang

= 6"

Gable overhang

= 6"

Panels

Profile

Panel lengths

Solid deck with underlayment

Turn off for panels screwed straight to purlins (pole barns, open sheds).

Panels to order

7× 14 ft

14-ft stock panels — cut each into two 6' 11" pieces for 14 roof panels · 7 per side × 2 sides · 36-in coverage · 97 lin ft of panel

Roof area: 288sq ft2.9 squares
Screws: 23180 per square, panels only
Panel run (cut): 6' 11"eave edge to ridge, along the slope
Panel weight: 201lb29 ga at 0.70 lb/sq ft

Trim & closures

Trim pieces and closure strips
Item	Length	Buy
Ridge cap	21 ft	3 × 10½ ft
Eave trim	42 ft	5 × 10½ ft
Rake trim	28 ft	3 × 10½ ft
Inside closures (eave)	42 ft	14 × 36 in
Outside closures (ridge)	42 ft	14 × 36 in

Compare panel profiles

Panels by profile
Profile	Panels	Lin ft	Panel cost
36-in rib panel36-in coverage	14	97	$392
5V crimp24-in coverage	22	152	$517

Screw pattern

Shopping list

7 panels 36-in rib panel panels, 14 ft stockcut each into two 6' 11" pieces · 7 per side at 36-in coverage · 97 lin ft$392
231 screws #14 × 1 in Woodtite roofing screws (OSB/plywood deck)80 per square; use #10 × 1½ in into purlins
3 pieces Ridge cap, 10½ ft × 14 in21 ft, lapped 6 in$111
5 pieces Eave trim / drip edge, 10½ ft42 ft
3 pieces Rake (gable) trim, 10½ ft28 ft
14 strips Inside foam closure, 36 in (eaves)$39.06
14 strips Outside foam closure, 36 in (ridge)$39.06
1 rolls Synthetic underlayment, 10-sq roll (42 in × 286 ft)$130
1 buckets 1-in plastic cap nails, bucket of 3,000$45.49

Estimated total$757

Cost estimate

Tap a price to use your store's

36-in rib panel panel, 14 ft (29 ga)
7 panels × $
$392
Ridge cap, 10½ ft
3 pieces × $
$111
Foam closure strips, 36 in
28 strips × $
$78.12
Synthetic underlayment, 10-sq roll (42 in × 286 ft)
1 rolls × $
$130
Plastic cap nails (3,000)
1 buckets × $
$45.49

Materials total$757

29 ga Galvalume prices from McCoy's (San Marcos, TX), Oct 23, 2026; cut-to-length uses the same per-foot rate. Eave and rake trim vary by supplier — get a quote with the panels.

Pitch

Panel length

Panels

Roof sq ft

Screws

Panel cost

3/12

6' 9"

281

226

$392

4/12

6' 11"

288

231

$392

5/12

7' 1"

296

237

$427

6/12

7' 4"

305

245

$427

8/12

7' 10"

328

263

$427

How this was worked out

Under 3/12 the IRC requires lap sealant on exposed-fastener panels; 36-in rib panels are rated down to 2½/12 by their makers and 5V crimp to 3/12. At 4/12 either profile is fine without sealant.

The full method, material data and tips are on the main metal roofing calculator page.