Singapore Post (SingPost) accepts a variety of shipping bags, such as plastic poly mailers and kraft paper envelopes, for domestic and international deliveries. However, to ensure your parcel is accepted at the post office, sorting facility, or self-service drop-off boxes like POPStation, you must adhere to strict size, weight, and material guidelines. For standard letterbox-bound services, such as Tracked Mail or Basic Package, the maximum packed dimensions are 324mm in length, 229mm in width, and 65mm in thickness, with a weight limit of 2kg. Larger or heavier shipments must go via parcel services like Speedpost, which accommodate up to 30kg.
Understanding these requirements before purchasing packaging materials prevents unexpected surcharges, delivery delays, or returned parcels. Selecting the correct bag size and material optimizes your shipping costs and ensures your items arrive safely at their destination.
Understanding Singapore Post's Size and Weight Limits
Singapore Post categorizes deliveries primarily into letterbox services and parcel services. This classification determines where your shipping bag is delivered and the postage cost. To have your package delivered directly to the recipient’s letterbox, you must use services like Basic Package or Tracked Mail. These services are highly convenient for local ecommerce transactions, as they do not require the recipient to be home.
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For these letterbox services, the absolute maximum dimensions for a packed shipping bag are 324mm (length) x 229mm (width) x 65mm (thickness), with a weight limit of 2kg. If your shipping bag exceeds these dimensions, it will not fit into standard HDB or private estate letterboxes, which is why SingPost strictly enforces these limits.
When your shipment exceeds the letterbox limits, it must go via SingPost’s parcel service, Speedpost. For Speedpost Standard or Express deliveries, the maximum weight limit is 30kg. The dimensional limits are also much larger: the maximum length must not exceed 1.5 metres, and the combined length and girth (length + 2 x width + 2 x height) must not exceed 3.0 metres.
A common pitfall is measuring shipping bags while they are flat. A flat poly mailer might measure 300mm by 220mm, which seems well within the letterbox limits. However, once packed with a bulky item, the bag bulges. This bulging increases the thickness while pulling the edges inward, reducing the effective length and width. Always measure your shipping bag after it is fully packed and sealed to ensure the final thickness does not exceed the 65mm limit.
Material and Packaging Restrictions
To withstand the mechanical stress of SingPost’s automated sorting machines, shipping bags must meet specific material standards. Standard opaque poly mailers made from co-extruded polyethylene plastic are highly recommended because they are strong, water-resistant, and tear-resistant. Heavy-duty kraft paper shipping bags are also acceptable and offer an eco-friendly alternative, provided they are thick enough to resist punctures.
Avoid transparent or semi-transparent shipping bags, as they are generally rejected for security and privacy reasons. Additionally, do not use flimsy, single-layer household plastic or grocery bags. These materials tear easily under tension, risk jamming the automated sorting belts, and offer virtually no protection for your goods.
Your shipping bags must also have a non-slip outer surface. Bags with highly slippery or glossy finishes can cause stacking issues on conveyor belts and sorting trays, leading to processing delays or damage if they slide off.
Sealing your shipping bags correctly is another critical requirement. The bag must be securely closed using the built-in, tamper-evident self-adhesive strip, or reinforced with heavy-duty packing tape. The seal must be completely flat and flush with the body of the bag. Loose flaps, protruding edges, or poorly taped openings can catch on sorting machinery, causing the bag to rip open.
If you reuse old shipping bags, you must completely remove, black out, or permanently cover all previous shipping labels, barcodes, addresses, and any hazardous material markings. Automated sorting systems rely heavily on barcode scanners; any old, visible barcode can cause the machine to misroute your package, leading to significant delivery delays.
How to Choose the Right Shipping Bags for Your Parcels
Choosing the right shipping bag requires translating SingPost’s official dimensions into practical purchasing decisions. When buying poly mailers, always account for the volume of your items. To calculate the correct flat bag size, add the thickness of your item to both the length and width of the item, then add an extra 20mm to 30mm safety margin. This margin ensures you can easily slide the item into the bag and seal it without putting excessive tension on the seams.
You must also decide between standard poly mailers and bubble-lined padded mailers. Standard poly mailers are excellent for non-fragile items such as clothing, apparel, and plush toys. They are lightweight, which helps keep your shipping weight low, and they do not add unnecessary bulk.
For semi-fragile items like books, stationery, phone cases, or small cosmetics, bubble-lined mailers are a much better choice. These mailers feature a built-in layer of bubble wrap that provides essential cushioning against impacts. Using a padded mailer eliminates the need to wrap the item in separate sheets of bubble wrap, helping you maintain a uniform shape and preventing the package from exceeding the 65mm letterbox thickness limit.
When sourcing shipping bags, always check their tensile strength and puncture resistance. High-quality poly mailers typically have a thickness of 50 to 60 microns. This thickness ensures the plastic will not split at the seams or puncture when packed with items that have sharp corners, such as hardcover books or boxed stationery.
Finally, verify that the outer surface of the shipping bag is compatible with adhesive labels. The material should have a matte or slightly textured finish that allows thermal shipping labels or paper address labels to stick firmly. Avoid bags with wax-like coatings, as the adhesive on SingPost shipping labels may peel off during transit, leaving your parcel unidentifiable.
Final Checks Before Dropping Off Your Parcel
Before you head to a post office, a POPStation, or a posting box, performing a quick verification routine can save you from costly surcharges or rejected packages. First, use a reliable ruler or measuring tape to check the final packed dimensions of your shipping bag, paying close attention to the thickness. Next, weigh the parcel on a calibrated digital scale to confirm it complies with your selected service’s weight limit.
Ensure the self-adhesive seal is fully intact and that there are no loose edges or open seams. The shipping label must be pasted flat on a single, smooth side of the bag. Do not wrap the barcode or address details around the edges of the bag, and ensure there are no creases or wrinkles running through the barcode, as this will prevent automated scanners from reading it.
For business owners or individuals purchasing shipping bags in bulk, it is highly recommended to consult the official Singapore Post website or speak with staff at a local post office counter. This ensures you have the most up-to-date specifications and guidelines before investing in a large inventory of packaging materials.
Frequently Asked Questions (FAQ)
Do shipping bags count as letterbox mail or parcels?
Shipping bags can qualify as either letterbox mail or parcels depending entirely on their final packed dimensions and weight. If a packed shipping bag is within 324mm x 229mm x 65mm and weighs under 2kg, it can be sent via letterbox services like Tracked Mail. If it exceeds any of these limits, it must be sent as a parcel via Speedpost.
Can I reuse old poly mailers for Singapore Post deliveries?
Yes, you can reuse old poly mailers, provided they are structurally sound, free of tears, and can be securely sealed with heavy-duty packing tape. You must completely cover, cross out, or remove all previous shipping labels, addresses, and barcodes to prevent automated sorting machines from misrouting your parcel.
What happens if my packed shipping bag exceeds the thickness limit?
If your shipping bag exceeds the 65mm thickness limit for letterbox services, it cannot be delivered to a standard letterbox. SingPost will either charge you a surcharge to upgrade the delivery to a parcel service, require manual processing at a counter, or reject the parcel entirely at automated drop-off points like POPStations.
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