My Roof Pitch

Metal Roofing Screws Calculator

Reviewed by the My Roof Pitch editorial team · Updated · Free, no sign-up, works offline after first load

Metal roofing needs roughly 70 to 80 screws per 100 square feet. Count purlin rows across the roof, multiply by screws per panel per purlin and by the number of panels. A 1,000 square foot roof with 36 inch panels on 24 inch purlins at 4 screws per row needs about 770 screws.

Key takeaways

  • Typical exposed-fastener roofs use 70–80 screws per square.
  • Closer purlins or high-wind edge zones increase the count.
  • Use #10 or #12 self-drilling screws with EPDM washers, length to penetrate the purlin ≥ 1 in.
  • Stitch (side-lap) screws are extra — about 1 every 24 in along each lap.

Your measurements

Enter the values you know — results update live.

Sloped roof area.

Net coverage, e.g. 36 in for most exposed-fastener panels.

On-centre spacing in inches.

Usually 3–4 in the field; edges and eaves get more.

Analysis

Live results from your measurements.

Live data
Screws needed
700
Bags of 250
3
Screws per square
67
Screws per sq ft
0.67
Show the working
  1. Area per fastening cell: 3 × 2 ft = 6 sq ft
  2. Screws per sq ft: 4 ÷ 6 = 0.667
  3. Total with waste: 1,000 × 0.667 × 1.05 = 700

What this calculator does

A metal roofing screws calculator estimates the fasteners for exposed-fastener panels such as R-panel, PBR and corrugated sheets. Each panel is screwed to every purlin it crosses, usually at the ribs or flats specified by the manufacturer, so the screw count depends on how many panel-purlin intersections the roof contains. This tool computes screws per square foot from panel width, purlin spacing and screws per intersection, then scales to your roof area with a waste allowance and rounds to bags of 250.

How to use it

  1. Enter the sloped roof area.
  2. Enter the net coverage width of one panel.
  3. Enter the purlin or batten spacing.
  4. Set screws per panel per purlin from the manufacturer's fastening pattern.
  5. Read total screws and bags; add stitch screws for side laps and trim screws separately.

The formula

Screws per square foot

screws/sq ft = screws per row ÷ (panel width ft × purlin spacing ft)

Each panel-purlin intersection covers one cell of panel width by purlin spacing.

Total

total = area × screws/sq ft × (1 + waste)

Waste covers dropped and stripped fasteners.

Worked example

1,200 sq ft barn roof, 36 in R-panel, purlins at 24 in, 4 screws per purlin, 5% waste.

  1. Cell = 3 × 2 = 6 sq ft
  2. 4 ÷ 6 = 0.667 screws/sq ft
  3. 1,200 × 0.667 × 1.05 = 840 screws

840 screws — four bags of 250.

Screws per square by purlin spacing (36 in panels)

Screws per square by purlin spacing (36 in panels)
Purlin spacing3 per row4 per row5 per row
16 in75100125
24 in506783
30 in405367
36 in334456
48 in253342
Screws per square by purlin spacing (36 in panels)

Common mistakes

  • Ignoring extra screws at eaves, ridges and edge zones required for wind uplift.
  • Forgetting stitch screws on side laps and trim screws on rake and ridge.
  • Over-driving screws so the washer splits and leaks.
  • Using screws too short to bite 1 in into timber purlins.

Assumptions and limits

  • Uniform fastening pattern across the field.
  • Exposed-fastener panels; standing seam uses concealed clips instead.
  • Trim and stitch screws are not included.

Frequently asked questions

How many screws per sheet of metal roofing?

A 3 ft wide sheet gets about 4 screws at every purlin. A 12 ft sheet over 24 in purlins crosses 7 purlins, so about 28 screws.

How many screws per square of metal roofing?

About 70–80 for typical 24 in purlins, closer to 100 at 16 in spacing.

Do you screw metal roofing on the rib or the flat?

Follow the manufacturer. Most exposed-fastener panels are screwed in the flat next to the rib into solid purlins; some corrugated systems specify the crown.

What size screws for metal roofing?

#10 or #12 self-drilling with a bonded EPDM washer, 1 to 1.5 in long into wood, or self-drilling tek screws for steel purlins.

How many screws in a bag?

Most roofing screws are sold in bags of 250 or buckets of 1,000.

How far apart are metal roofing screws?

Across the panel they follow the rib pattern, typically 9 to 12 in; along the panel they are at every purlin, 24 in or less.

Do I need more screws in high wind areas?

Yes. Edge and corner zones often need screws at every rib and closer purlins per ASCE 7 uplift design.

How many stitch screws do I need?

Roughly one every 20–24 in along each side lap, so about 6 per 12 ft lap.

Related guides

Last updated 2026-10-08. Results are estimates for planning and are not a substitute for a licensed engineer or local code review.