Work out how many EPDM or TPO rolls your flat roof needs. The calculator lays out real roll sizes on your roof and counts sheets, seams, splice tape and wall flashing, so you can check a material list before you buy.
Roll sizes and overlaps come from manufacturer data sheets and details. See “How we calculate”.
Lay out sheets on a rectangular roof and count rolls, seams and seam tape.
Single-ply membranes come in rolls a fixed width wide and usually 100 ft long. Wider sheets mean fewer seams, and seams are where most single-ply leaks start. These are the sizes on the data sheets we checked:
| Product | Widths | Length | Thickness |
|---|---|---|---|
| Carlisle Sure-Tough reinforced EPDM | 10 ft standard; 6.5 ft perimeter sheets | 100 ft | 45, 60, 75 mil |
| Elevate UltraPly TPO Platinum | 5 ft, 6 ft 2 in, 8 ft, 10 ft, 12 ft 4 in (white only) | 100 ft | 80 mil |
| Johns Manville JM TPO-SA (self-adhered) | 10 ft | 100 ft | 60 mil |
| Elevate QuickSeam EPDM splice tape | 3 in or 6 in | 100 ft | 0.025 in |
Narrower perimeter sheets exist because the edges and corners of a roof take the highest wind uplift. Carlisle says its 6.5-ft sheets are used as perimeter sheets and to reach certain uplift ratings. Your roofer’s wind design decides where they go. This calculator lays out one roll width across the whole roof.
Every number above comes from the steps below — the same formula and constants the calculator runs, so you can check it yourself.
| Setting | Default | Source |
|---|---|---|
| EPDM roll widths | 10 ft, 6.5 ft | Carlisle Sure-Tough data sheet |
| TPO roll widths | 5, 6.17, 8, 10, 12.33 ft | Elevate UltraPly TPO Platinum sheet; JM TPO-SA (10 ft) |
| Roll length | 100 ft | All three membrane data sheets |
| EPDM seam overlap | 3 in minimum | SPRI field-splice guideline (“or a dimension required by the systems supplier”) |
| TPO overlap, adhered | 3 in minimum | Tremco side lap detail DWG 80 |
| TPO overlap, mechanically attached | 6 in | Tremco side lap detail DWG 78 (plates and screws in the lap) |
| Splice tape roll | 3 in or 6 in × 100 ft | Elevate QuickSeam data sheet |
| Flashing carried onto the roof | 6 in | Our assumption |
Roll sizes, tape sizes and overlaps come from the manufacturer and industry documents below, which we opened and checked in October 2026. Always follow the details for the specific system you buy.
Last reviewed: October 2026.
EPDM is a cured rubber, so its seams are glued, not welded. The SPRI guideline for taped EPDM splices calls for at least a 3-inch overlap, a cleaned and primed splice area, splice tape at least 2 inches wide, and a small edge of tape left showing so the installer can see the splice is complete. Carlisle sheets can come with tape already applied at the factory. Elevate sells field splice tape in 3-inch and 6-inch rolls, each 100 ft long.
TPO is a thermoplastic, so overlapping sheets are fused with hot air. Tremco’s details show a 3-inch minimum overlap for adhered TPO and a 6-inch overlap for mechanically attached TPO, where the plates and screws sit inside the lap under the weld.
| EPDM | TPO | |
|---|---|---|
| How seams are made | Primer + splice tape | Hot-air welded |
| Typical overlap | 3 in minimum (SPRI) | 3 in adhered / 6 in mechanically attached (Tremco details) |
| What the calculator counts | Rolls of splice tape | Linear feet of weld |
Comparing costs? See the EPDM roof cost calculator and the TPO roof cost calculator. Before you order, check that the roof drains with the flat roof slope calculator.
Tell us about your flat roof project and we'll match you with up to 3 licensed local roofers. Compare prices and pick the best deal — the choice is 100% yours.
Carlisle’s standard Sure-Tough reinforced EPDM sheet is 10 ft × 100 ft (1,000 sq ft), with 6.5-ft-wide sheets for perimeters. Other EPDM lines come in other sizes, so check the data sheet of the product you buy.
Elevate’s UltraPly TPO Platinum comes 100 ft long in 5 ft, 6 ft 2 in, 8 ft, 10 ft and 12 ft 4 in widths. Johns Manville’s JM TPO-SA comes in 10 ft × 100 ft rolls.
The SPRI guideline for taped EPDM splices calls for a minimum 3-inch overlap, or whatever the system manufacturer requires.
In Tremco’s details, adhered TPO overlaps at least 3 inches. Mechanically attached TPO overlaps 6 inches so the plates and screws fit inside the lap.
Splice tape comes in 100-ft rolls (3 or 6 in wide), so divide the total seam length by 100 and round up. A 40 × 30 ft roof laid with 10-ft sheets has about 120 ft of seams, which is 2 rolls.
Sheets overlap at every seam, rolls rarely divide evenly into your roof length, and wall flashing needs material too. The offcuts are used for flashing first, but some waste is normal.