Standard outside dimensions are a useful cross-check, not a substitute for measuring the real unit, attached hardware, and the coverage path.
A container top cover is much smaller than a full drape. Decide whether the tarp covers only the roof, reaches below the top rail, clears doors, or wraps stored equipment beside the container.
Standard outside dimensions
Hapag-Lloyd’s ISO-based specification lists 20-foot and 40-foot general-purpose containers at 8 ft wide and 8 ft 6 in high; high-cube height is 9 ft 6 in. Published metric lengths are 6,058 mm for 20 ft and 12,192 mm for 40 ft. Production tolerances and attached features still make field measurement necessary.
| Type | Nominal outside size | Use as |
|---|---|---|
| 20 ft standard | 20 × 8 × 8 ft 6 in | Planning check |
| 40 ft standard | 40 × 8 × 8 ft 6 in | Planning check |
| 40 ft high cube | 40 × 8 × 9 ft 6 in | Planning check |
Choose the coverage path
- Top only: roof length and width plus edge allowance.
- Top and partial sides: add the actual drop on both sides and both ends.
- Full drape: add two full height drops in each direction, plus working allowance.
Calculate, then check handling weight
For a rectangular full drape: tarp length = container length + two end drops + allowance; tarp width = container width + two side drops + allowance. A full 40-foot cover becomes very large, especially in high-mass fabric. Plan how it will be lifted and positioned before buying.
Worked example: 40 ft full drape
A standard 40 ft container is nominally 40 ft long, 8 ft wide, and 8 ft 6 in high. For a full drape with a small working allowance, the tarp length becomes 40 + 8.5 + 8.5 + allowance, or about 58 ft; the width becomes 8 + 8.5 + 8.5 + allowance, or about 26 ft. That is roughly 1,500 sq ft of fabric. At 610 GSM (about 18 oz/yd²), the base material alone weighs close to 200 lb before hems and hardware, which is why large container covers are usually handled as panels with planned overlaps rather than one sheet.
Doors, castings, and sharp corners
Record corner castings, locking bars, vents, door swing, roof repairs, and anything attached above the nominal envelope. Protect contact points and form drainage so water cannot collect in a broad unsupported pocket.
Important limits
A loose cover is not a structural roof, shipping-container repair, engineered wind restraint, or approved transport system. Do not climb on container roofs without a safe-access and fall-protection plan.
Dimensions source: Hapag-Lloyd Container Specification, based on ISO 668 dimensions.
Frequently asked questions
What size tarp do I need to cover a 20 ft shipping container?
For a top-only cover, plan the roof footprint of roughly 20 × 8 ft plus edge allowance on all sides, which usually lands near a 24 × 12 ft sheet. A full drape to the ground needs two height drops of about 8 ft 6 in in each direction, producing a far larger cover. Measure the actual unit before ordering.
What size tarp covers a 40 ft container completely?
A full drape over a standard 40 ft container needs the length plus two end drops and the width plus two side drops of roughly 8 ft 6 in each, which works out to a sheet on the order of 57 × 25 ft before working allowance. High-cube units add another foot of drop. Covers this size are extremely heavy and need a handling plan.
Can I use the published container dimensions instead of measuring?
Use them as a cross-check only. ISO-based nominal dimensions are reliable for the basic envelope, but repairs, attached hardware, vents, and door hardware change the real coverage path. A few inches of error at each edge compounds across a 40 ft cover.
Is a tarp a good long-term roof for a container?
A tarp is temporary water management, not a structural roof. Unsupported spans collect water, fabric fatigues at contact points, and wind works the sheet loose. For long-term protection, plan drainage, support, and inspection, or consider a purpose-built shelter.
How do I keep water from pooling on a container cover?
Create a slope or ridge so water runs off an edge, support broad spans, and tension the cover so pockets cannot form. A single deep water pocket on a 40 ft roof can weigh hundreds of pounds and damage the cover or the roof.
How this guide was prepared
We separate geometry and unit conversions from product claims, use exact standards where available, and flag specifications that vary by manufacturer. See our editorial policy for the review process.