Accurate custom tarp sizing starts with the object, then adds the exact drop, overlap and fixing reach the installation needs. This guide shows how to build a finished-size specification for flat covers, truck tarps, equipment covers, curtains and irregular shapes.
A common sourcing mistake is sending one number such as “10 × 12 ft” without saying what it represents. That figure could mean the object size, the desired coverage area, the finished tarp size or the raw cut size before hems and seams.
For made-to-measure work, the most useful approach is to send both the object dimensions and the finished dimensions you need after fabrication. The fabricator can then plan hems, welded seams, reinforcement and panel layout without shrinking the usable cover by accident.
For background on tarp materials and terminology, see DERFLEX's tarpaulin material guide and PVC tarpaulin overview.
For dimension-critical projects, also define the measurement condition and acceptable finished-size tolerance on the approved drawing.
Use this sequence for custom PVC tarps, truck and trailer covers, machinery covers, outdoor storage covers, curtains and repeat OEM programs.
Start by identifying the object and the installation method: flat cover, draped cover, fitted enclosure, truck load, curtain panel, canopy, roof sheet or equipment cover. Note whether the tarp is secured by ropes, bungees, rails, hooks, lacing, grommets, D-rings, webbing, sleeves or a mechanical roll system.
Use the longest and widest points rather than a nominal equipment or truck-bed size. Include handles, pipes, corners, brackets, raised loads and other protrusions if the tarp must pass over them. For a frame, measure the actual outer edges and not only the spacing between posts.
If the tarp hangs down a side, measure from the top edge to the intended finished edge or fixing line. For curved, sloped or arched surfaces, run a flexible tape along the actual path the fabric will follow; a horizontal projection can underestimate the required size.
Extra material should have a purpose: weather overlap, fastening reach, access flap, wrap-around coverage, drainage or installation clearance. Oversizing without a reason can create sagging, flapping, abrasion and water pockets.
For a rectangular frame or opening, measure both corner-to-corner diagonals. If they differ, the frame is not square. Record the two diagonal values instead of forcing a nominal rectangle; this can be important for canopy panels, curtains and fitted covers.
Mark grommet or D-ring centers from a fixed datum. Also show seams, straps, webbing, sleeves, rope hems, zippers, clear windows, cut-outs and high-wear corners. Hardware spacing should match the actual support structure rather than a generic interval. DERFLEX can discuss reinforcement and hardware options for custom tarp manufacturing.
Create a top view and side view with labeled dimensions, units and revision number. For irregular shapes, add front/rear views or sections where needed. Photos are useful for showing obstacles and installation conditions, while the drawing should carry the dimensions used for production and approval.
These formulas create a starting finished tarp size. Do not add a guessed factory hem allowance; the production team should calculate raw cut panels, seam overlap and hem consumption from the finished specification.
Useful for pallets, flat storage, temporary roof protection and simple rectangular covers.
Use measured drops that reach the intended tie-down line rather than a universal “extra” allowance.
Measure along arches, slopes and rounded loads with a flexible tape, then show the profile in a side-view drawing.
Enter the top or flat-area dimensions plus the overlap or drop required at each edge. Use one unit consistently.
Enter measurements to create a copy-ready quotation line.
| Application | Key Measurements | Critical Details to Mark | Procurement Note |
|---|---|---|---|
| Truck & trailer tarps | Tray or load length/width, cargo height, front/rear drop, side drop, bow profile if applicable | Tie rail location, grommet/D-ring rows, rear flap, seam route, high-wear corners | Size, reinforcement and fixing layout should be reviewed together. See truck tarpaulin options. |
| Industrial machinery cover | Maximum length, width, height and surface path over protrusions | Handles, pipes, vents, access panels, sharp edges, lifting points and clearance | Consider local reinforcement where the cover rubs against hard corners. |
| Five-sided box cover | Top length, top width, each side height; confirm whether all side drops are equal | Open bottom, zipper/closure side, lifting handles, corner construction, ventilation | For close fit, a panel drawing is better than only L × W × H. |
| Warehouse curtain / partition | Opening width and height, rail position, floor clearance, overlap | Center split, side overlap, hanging points, clear window, access door and bottom weight | Measure from the actual installed track or support datum. |
| Canopy / frame tarp | Outer frame dimensions, pitch, slope, ridge length and diagonals | Fixing gap, lacing points, tension direction, posts, gutters and drainage | Do not assume frame footprint equals tarp surface path. |
| Agricultural / stockpile cover | Pile footprint, maximum height, slope and anchoring area | Ground fastening, sandbag line, wrap direction, overlap and drainage route | A larger tarp is not automatically safer if excess material can flap or pool. |
A simple hand sketch is often enough if it is dimensioned clearly. For repeat orders or exact-fit covers, use a revision-controlled drawing so later production follows the same approved geometry.
For B2B programs, add the required measurement condition—such as “laid flat and relaxed”—and ask the supplier to confirm a project-specific tolerance before production.
Material width, seam layout, edge reinforcement and hardware all influence how a measured tarp becomes a finished product. These DERFLEX images show the coated fabric, finished truck-cover use and reinforced eyelet detail that buyers should consider when preparing a specification.
Most sizing problems begin before production. These errors can make a tarp hard to install even when the fabric itself is suitable.
Catalog dimensions may exclude attachments, rails or raised loads. Measure the actual object in its working configuration.
A purchase order should say exactly which stage the dimension represents. For installation, finished size is usually the clearest basis.
Universal allowances can create too much or too little material. Measure the real drop, overlap or tie-down reach instead.
Measure along the fabric path. A flat projection can understate the material required over an arch or rounded load.
Grommets and D-rings should align with the actual support structure and pull direction, not only a default spacing rule.
Photos explain context, but production still needs dimensions, reference points and revision-controlled details for repeatability.
The clearer the brief, the easier it is to compare quotations on the same basis and avoid size assumptions.
Product: Custom PVC coated polyester tarp
Quotation basis: FINISHED SIZE after all hems and welded/sewn seams
Finished dimensions: [Length] × [Width] [unit]
Measurement condition: Laid flat and relaxed / fitted to reference frame (specify)
Hardware: Positions and quantity per attached drawing
Material: [Target GSM / duty level / color / required performance]
Quantity: [Qty]
Approval: Please confirm proposed finished-size tolerance and fabrication details before production.
DERFLEX can support custom finished tarps and related custom PVC tarp solutions, while buyers sourcing roll goods can review PVC coated fabric.
Very large finished dimensions may require multiple fabric panels. Seam position can affect drainage, folding, appearance and local stiffness, so a large tarp drawing should allow the fabricator to review the panel plan.
Grommets alone do not define edge strength. Repeated wind or tie-down loads may require webbing, reinforced hems, corner patches or project-specific load distribution.
The heaviest fabric is not automatically the best. Handling frequency, abrasion, outdoor exposure, temperature, folding and installation method all influence a practical material choice. Compare super heavy duty tarps only when the application warrants the added structure.
For exact-fit or repeat OEM programs, define how overall size, diagonals and hardware centers will be checked. Keep the approved drawing revision with the order records.
Measure the object first, then calculate the coverage required by adding the actual drop, overlap or fastening reach. For a custom quotation, provide both the object measurements and the required finished tarp dimensions so the production basis is clear.
Cut size is the raw material dimension before hems, seams and other fabrication consume material. Finished size is the completed usable dimension after production. For made-to-measure installation, specifying the finished size is usually the clearer approach.
There is no single universal allowance. Measure from the top or coverage edge to the location where the tarp actually needs to end or connect to its fastening system. Add only the functional overlap or drop required for weather protection, tying, access or wrap-around coverage.
Break the geometry into simple sections and label every side, diagonal, curve, slope, cut-out and fixing point. Use a flexible tape along curved surfaces and send top, side and detail views. Photos help explain the object, while the dimensioned drawing should control production.
Measure the top length and width, then the required drop for each of the four sides. If the sides are not equal, record them separately. Mark protrusions, openings, zippers, handles, vents and any corner or edge that needs reinforcement.
Review size and hardware layout together. Mark grommet or D-ring centers from a fixed datum so they align with hooks, rails or structural supports. Avoid assuming a generic spacing if the installation has fixed anchor points.
Large covers may be fabricated from multiple fabric panels depending on roll width, finished size and production method. For large or dimension-critical tarps, ask the manufacturer to review seam layout, reinforcement, handling and packing from the drawing before production.
Send the application, finished dimensions, object measurements, drawing/photos, quantity, material or GSM target, color, performance requirements, seam and edge construction, grommet/D-ring layout, printing/packing needs, destination and any required tests or documentation.
Send DERFLEX the object dimensions, required finished size, installation photos, material direction and fixing-point layout. For irregular or repeat-order projects, include a dimensioned drawing so the quotation can be based on the same specification you expect to receive.