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PVC Strip Curtain Sizing & Calculation Guide — How to Measure Correctly
Correct sizing is the foundation of a successful PVC strip curtain installation. An undersized curtain leaves gaps that negate thermal and hygiene performance; an incorrectly specified strip width or thickness results in inadequate barrier performance or unnecessarily difficult passage. This guide provides definitive, step-by-step measurement and calculation methodology for every scenario — from simple pedestrian doorways to complex cold room and forklift access configurations — with worked examples, reference tables, and common mistakes to avoid.
This guide forms part of our comprehensive reference library: Complete Guide to PVC Strip Curtains | Grades & Materials Guide | Rail Systems Guide | Regulations & Standards | Applications Directory
Why Correct Sizing Matters
Energy Efficiency
A strip curtain that does not fully cover the door opening will have gaps through which unconditioned air moves freely — undermining the entire purpose of the installation. In a cold room application, even a 100mm gap at the side of the curtain can negate 20–30% of the thermal barrier performance. Correct sizing, including appropriate side overhang and floor clearance, is as important as grade selection in achieving the expected energy savings.
Safety
Under PUWER (Provision and Use of Work Equipment Regulations 1998) and the Workplace (Health, Safety and Welfare) Regulations 1992, barriers must adequately separate pedestrian and vehicle traffic zones and must not create new hazards. A curtain that is too narrow, leaving the sides of the opening exposed, may create a false sense of a complete barrier whilst leaving unsafe gaps. Strips that are too long and drag on the floor create trip hazards.
Appearance and Performance
Correctly sized curtains hang vertically and straight, with consistent overlap throughout their width. Strips that are too heavy for the application may not return to position after being displaced; strips that are too light may billow in draughts. The correct combination of strip width, thickness, and overlap creates a professional, functional installation that performs consistently over its service life.
Step 1: Measuring Your Door Opening
Clear Width
Measure the clear opening width — the distance between the inner faces of the door frame (or the structural opening if there is no frame). This is the width that traffic actually passes through. Do not measure the outer frame dimension. Take the measurement at the widest point of the opening — some door frames have reveals that widen toward the face of the wall.
Important: The rail should be equal to, or slightly greater than, the clear opening width. The strip curtain should extend slightly beyond the opening edges on each side (typically 50–75mm per side overhang) to seal against the doorframe reveals. Therefore, the total curtain width = clear opening width + 100–150mm.
Clear Height
Measure the clear opening height — from the underside of the lintel or soffit down to the floor level at the threshold. In situations with an uneven threshold or a ramp, measure to the highest point of the floor at the opening. Strip length should equal this height, with strips hanging to within 20–50mm of the floor (not dragging).
Where to Measure
Always measure at the face of the opening, not inside a reveal. If the opening has a stepped or raked threshold, measure to the worst-case floor height (the highest point) to ensure the curtain seals at all points. For outdoor openings, allow for the possibility of pooled water or ice at the threshold — a slightly shorter strip may be preferable to one that freezes to the floor in winter.
Step 2: Choosing Strip Width
| Strip Width | Recommended Traffic Type | Typical Door Width | Ease of Passage | Material Cost | Notes |
|---|---|---|---|---|---|
| 100mm | Pedestrian (light, infrequent) | Up to 1000mm | Very easy | Lowest | Small rooms, cupboards, internal partitions |
| 200mm | Pedestrian (regular), pallet truck | 1000–2500mm | Easy | Low | Most common; standard warehouse/factory/retail |
| 300mm | Forklift (light to medium), pallet truck | 2000–3500mm | Moderate | Medium | Standard industrial; best balance for forklift access |
| 400mm | Forklift (heavy), HGV, large machinery | 3000–5000mm | Requires vehicle | Highest | Loading docks, vehicle access bays, large openings |
Key principle: Wider strips mean fewer strips to hang, less material to replace individually, and better performance per unit area. However, wider strips are heavier and may be harder for pedestrians to displace manually. For mixed pedestrian and forklift traffic, 300mm is often the best compromise — easy enough for pedestrians, robust enough for forklifts.
Step 3: Choosing Strip Thickness
| Thickness | Traffic Type | Application | Rigidity | Service Life (typical) |
|---|---|---|---|---|
| 2mm | Pedestrian only | Offices, retail, light industry, small openings | Flexible, easy to displace | 3–7 years (light traffic) |
| 3mm | Pedestrian + pallet truck | Warehouses, food factories, general industrial | Medium rigidity, good hang | 3–5 years |
| 4mm | Forklift + heavy traffic | Loading docks, large warehouse, heavy industrial | Stiff, excellent hang/return | 3–6 years (high traffic) |
Thickness and temperature: For cold room applications at -15°C to -30°C, use polar grade 3mm or 4mm. Standard 2mm polar grade may be used in -5°C to -15°C cold stores but 3mm provides better hang and seal in very cold environments where the PVC stiffens slightly even in polar grade.
Step 4: Calculating Overlap
Overlap ratio is the percentage of strip width by which each strip overlaps its neighbour. The two standard configurations are:
50% Overlap (Standard / Pedestrian)
Each strip overlaps its neighbour by half its width. For 200mm strips: 100mm overlap. This is the most common configuration for ambient-temperature pedestrian and light vehicle applications. It provides effective air and thermal separation whilst requiring modest force to push through.
Example: 200mm wide strips, 50% overlap → each strip's edge-to-edge spacing is 100mm (the strips are offset by 100mm = 50% of 200mm).
100% Overlap (Double / Forklift / Cold Store)
Each strip entirely covers the strip behind it — the overlap equals the full strip width. From the front, you see a single unbroken curtain; from the side, you can see two strips at every point. This configuration doubles the air barrier effectiveness, dramatically improves cold store performance, and provides the mass required for consistent self-closing in forklift environments.
Example: 300mm wide strips, 100% overlap → each visible strip position has a strip directly behind it; the edge-to-edge spacing of successive strips is effectively zero from the front.
Other Overlap Ratios
Some specifications use 33% or 66% overlap as intermediate configurations. For standard applications, stick to 50% or 100% as these are the industry norms with well-established calculation methods and compatible rail hook spacings.
Step 5: Calculating Number of Strips
Formula for 50% Overlap
Number of strips = (Clear opening width + side overhang × 2) ÷ (strip width × 0.5) + 1
Simplified for 50% overlap: divide the total curtain width by half the strip width, then add 1.
Worked example (50% overlap):
- Door width: 2000mm
- Side overhang: 75mm each side → total curtain width: 2150mm
- Strip width: 200mm
- 50% overlap pitch: 100mm
- Number of strips: 2150 ÷ 100 + 1 = 22.5, round up to 23 strips
Formula for 100% Overlap
For 100% overlap, you need to calculate two layers of strips. The number of strips per layer is calculated as for 50% but using the full strip width as the pitch. The total strip count is then doubled (two layers).
Number of strips per layer = (Total curtain width ÷ strip width) + 1
Total strips = strips per layer × 2
Worked example (100% overlap):
- Door width: 3000mm
- Side overhang: 75mm each side → total curtain width: 3150mm
- Strip width: 300mm
- Strips per layer: 3150 ÷ 300 + 1 = 11.5, round up to 12
- Total strips (2 layers): 12 × 2 = 24 strips
Step 6: Calculating Total Material Length
Once you know the number of strips, calculating total material required is straightforward:
Total strip length (metres) = Number of strips × (door height + fixing allowance)
The fixing allowance accounts for the portion of the strip above the door height that is clamped in the hook or rail fitting, typically 150–200mm. Add 200mm to the door height for each strip.
Worked example:
- Door height: 2500mm (2.5m)
- Fixing allowance: 200mm → strip length per strip: 2700mm (2.7m)
- Number of strips: 23 (from step 5 example)
- Total material: 23 × 2.7m = 62.1 linear metres
When ordering from bulk roll stock, round up to the nearest whole metre and add 5–10% contingency for measurement tolerance and any required re-cuts.
Step 7: Measuring for the Rail
Rail Length
Rail length = clear opening width (do not add the side overhang allowance — the strips themselves overlap the opening edges, not the rail). If the rail must fit within a door reveal, measure the reveal width and note that you will need side seals to fill the gap between strip edges and doorframe.
Fixing Points
Number of fixing points = (rail length in mm ÷ 600) + 1, rounded up. For a 2000mm rail: (2000 ÷ 600) + 1 = 4.3 → 5 fixing points. Space them equally, with fixings at each end.
Height Positioning
The underside of the rail should be at the same height as the underside of the door lintel or opening soffit. This positions the top of the PVC strips flush with the opening header — no gap above the curtain. If the rail mounting system adds height (e.g., a swivel hinge bracket), account for this in the rail positioning calculation.
Ceiling/Wall Clearance
Allow at least 50mm clearance above the rail for fixing access. For swivel hinge rails, allow clearance for the full arc of travel (at least 200mm in front of the wall for the rail to swing out freely).
Common Sizing Mistakes (and How to Avoid Them)
| Mistake | Consequence | How to Avoid |
|---|---|---|
| Measuring outer frame instead of clear opening | Curtain too wide, won't fit or looks bunched | Always measure between inner edges of the frame |
| Forgetting side overhang | Gaps at curtain edges; thermal and hygiene failure | Always add 50–75mm overhang each side |
| Strips too long (dragging on floor) | Rapid wear, trip hazard, strips pulled off hooks | Measure to floor, allow 20–50mm clearance at bottom |
| Strips too short (gap at floor) | Draught, thermal loss, pest ingress at floor level | Measure at actual threshold height; allow for uneven floors |
| Using 50% overlap for forklift access | Strips fail to self-close; poor thermal performance | Always specify 100% overlap for forklift access |
| Using standard PVC in freezer (-10°C or below) | Strips crack, become brittle, fail to self-close | Specify polar/freezer grade for any below-5°C application |
| Under-specifying strip thickness | Rapid wear, poor hang, excessive displacement from draught | Use 3mm minimum for pallet truck; 4mm for forklifts |
| Rail shorter than opening width | Exposed gaps at sides of curtain | Rail length = clear opening width (plus overhang strips) |
| Insufficient fixing points | Rail sags or deflects under strip weight | Fix at maximum 600mm centres; never exceed max span for rail type |
| Not allowing for door reveal depth | Curtain set too far back; thermal seal poor at edges | Position rail at the face of the opening, not in the reveal |
Worked Examples Table
| Door Width | Door Height | Traffic Type | Strip Spec | Overlap | Strip Count | Total Linear Metres | Grade |
|---|---|---|---|---|---|---|---|
| 1200mm | 2100mm | Pedestrian | 200mm × 2mm | 50% | 14 | 32.2m | Standard clear |
| 1200mm | 2100mm | Pallet truck | 200mm × 3mm | 50% | 14 | 32.2m | Standard clear |
| 1200mm | 2100mm | Forklift | 300mm × 4mm | 100% | 18 | 41.4m | Heavy duty |
| 2000mm | 2500mm | Pedestrian | 200mm × 2mm | 50% | 22 | 59.4m | Standard clear |
| 2000mm | 2500mm | Pallet truck | 200mm × 3mm | 50% | 22 | 59.4m | Standard clear |
| 2000mm | 2500mm | Forklift | 300mm × 4mm | 100% | 30 | 81.0m | Heavy duty |
| 3000mm | 3500mm | Pedestrian | 300mm × 2mm | 50% | 22 | 80.3m | Standard clear |
| 3000mm | 3500mm | Pallet truck | 300mm × 3mm | 50% | 22 | 80.3m | Standard clear |
| 3000mm | 3500mm | Forklift (heavy) | 400mm × 4mm | 100% | 32 | 116.8m | Heavy duty |
Strip count includes 75mm side overhang each side. Linear metre totals include 200mm fixing allowance per strip.
Standard Door Sizes Reference Table
| Door Type | Typical Width | Typical Height | Recommended Strip Width | Recommended Thickness | Typical Application |
|---|---|---|---|---|---|
| Single personnel door | 900mm | 2100mm | 100–200mm | 2mm | Office, retail, small room |
| Double personnel door | 1800mm | 2100mm | 200mm | 2–3mm | Commercial, warehouse pedestrian |
| Standard industrial door | 2000–2500mm | 2200–2500mm | 200–300mm | 3mm | Light industrial, pallet truck access |
| Warehouse vehicle door | 3000–4000mm | 3000–4000mm | 300–400mm | 3–4mm | Forklift access |
| Loading dock door | 3000–4000mm | 4000–5000mm | 400mm | 4mm | HGV, large forklift |
| Cold room door | 1800–2500mm | 2200–2500mm | 200–300mm | 3mm | Polar grade, 100% overlap |
| Blast freezer door | 1500–2000mm | 2000–2500mm | 200–300mm | 3–4mm | Polar grade, 100% overlap, twin track |
| Agricultural barn door | 3000–6000mm | 3500–5000mm | 300–400mm | 3–4mm | Vehicle/machinery access |
Cold Room Sizing Considerations
Increased Overlap for Temperature Differential
For cold rooms operating below -15°C, or blast freezers below -25°C, the temperature differential between the two sides of the curtain creates significant density-driven airflow (cold, dense air sinks out of the opening whilst warm air is drawn in above). This phenomenon is stronger than the airflow addressed by standard thermal calculations for ambient applications. To compensate:
- Specify 100% overlap minimum for any opening where the temperature difference exceeds 20°C
- Consider twin-track rails with two independent polar-grade curtain layers for blast freezers
- Ensure floor seal is correct — use brush seals at the floor junction if the floor surface is uneven
- Specify extra side overhang (100mm per side rather than 75mm) to seal against the door reveal
Condensation Strips
At the transition between cold and ambient air, condensation forms on the PVC strips — a normal phenomenon that does not indicate a problem. In HACCP-compliant food environments, the condensation zone on the cold side of the curtain must be managed to prevent water dripping onto product. Positioning the curtain slightly on the warm side of the threshold (rather than centrally in the opening) moves the condensation zone away from the product storage area.
Floor Clearance in Cold Rooms
In cold rooms with anti-condensation floor heating or slightly raised threshold profiles, adjust the floor clearance calculation accordingly. Strips should not touch the floor — this causes rapid wear and in freezer conditions may cause the strip to freeze to the floor surface. A 30–50mm clearance is appropriate for cold room applications.
Forklift Clearance Heights
When sizing strip curtains for forklift access, the vertical profile of the forklift and its load must be considered:
| Forklift Type | Typical Maximum Height (mast up, loaded) | Recommended Minimum Door Clear Height | Minimum Strip Length |
|---|---|---|---|
| Counterbalance FLT (standard) | 3500–4500mm | 4000–5000mm | Door height + 200mm fixings |
| Reach truck | 3000–4000mm | 3500–4500mm | Door height + 200mm fixings |
| Pallet truck (manual) | 300mm (pallet + product) | 2200mm (standard) | Door height + 200mm fixings |
| Pallet truck (electric ride-on) | 1800mm (driver + load) | 2500mm | Door height + 200mm fixings |
Impact zone consideration: The most likely point of strip curtain impact from a forklift is at mid-height — typically 1500–2500mm above floor level — where the forks, load, and front face of the truck are at their widest. Strips in this zone experience the highest impact frequency and wear fastest. For heavy forklift traffic, consider specifying 4mm heavy duty strips only in the impact zone (bottom 2500mm of strips) whilst using 3mm above, or specify full-height 4mm throughout for simplicity.
How to Order
Made to Measure
Our made-to-measure service takes the calculation work out of ordering. Simply provide: door clear width, door height, grade required, strip width, strip thickness, overlap specification, and rail type. We pre-cut strips to the correct length, pre-fit hooks, calculate the correct strip count, and supply complete with rail and all fixing hardware. Delivery 2–5 working days.
Bulk Rolls
Order PVC strip material by the metre from bulk rolls for large installations, ongoing replacement stock, or facilities that prefer to cut to length on-site. Available in 25m and 50m rolls in all grades and dimensions.
Blank Strip by the Metre
Individual pre-cut strip lengths without hooks are available from our blank PVC strip by the metre range. Ideal for replacement of individual strips in an existing installation — simply measure the existing strip length and order the same grade and width.