Last updated: September 23, 2026 | By XHX Metal Engineering Team
Parcel box dimensions decide whether a product works before any other specification matters. A box that is 20 mm too shallow will not take the parcel the customer actually receives, and a box that is 60 mm too deep costs more in material and freight on every unit of a programme that may run for years.
This guide is written for the buyers who have to fix those numbers. It covers the three dimensions that actually control a parcel box, the slot geometry that keeps a parcel out of reach, the sizes that suit a porch, an apartment entrance and a trade counter, and how a programme runs from drawing to delivery — with real batch data from three supplier programmes.
Figure 1: A wall mounted parcel box, with the top letter slot and the lower lockable access door that set its working dimensions.
The Product: What Parcel Box Dimensions Actually Describe
Why Dimensions Decide Whether the Product Sells
Parcel box dimensions are not one measurement but three working numbers: the slot opening that a courier posts through, the internal chamber that holds the parcel, and the access door that the owner opens to retrieve it. Get the first two wrong and the product fails on the doorstep rather than in the factory.
The commercial reason to fix them early is cost. A parcel box dimensions decision flows straight into the flat pattern, the sheet size, the coating area and the packed carton, so every 10 mm added to depth is paid for on every unit in the programme. Buyers who test the dimensions against real parcels before the drawing is released spend less than buyers who discover the problem after the first delivery.
The Three Numbers: Slot, Chamber, and Access Door
The slot is the opening at the top, usually a horizontal letter slot with a rain lip above it. Its clear width and height set the largest parcel a courier can post, and they are always smaller than the chamber behind it because the parcel has to pass through at an angle.
The chamber is the internal volume, and its usable size is further reduced by the retrieval flap and by any internal baffle. The access door is the lower opening the owner uses, and it sets the largest parcel that can be taken out again. A parcel box dimensions set is only consistent when the door opening is at least as large as the slot, so that anything posted can be retrieved.
Figure 2: The letter slot opened, showing the internal retrieval flap that reduces usable chamber volume.
The Dimensions Buyers Get Wrong
The most common mistake is quoting the external size. A parcel box dimensions sheet that lists 400 x 300 x 200 mm as an outside measurement tells the buyer nothing about whether a 320 mm parcel fits, because wall thickness, the flap and the door frame all take space out of the chamber.
The second mistake is ignoring the parcel that actually arrives. Couriers deliver boxes, padded envelopes and bags in a wide spread of shapes, and a slot sized for the average parcel will still reject the awkward one. Buyers should test their parcel box dimensions against a sample of real deliveries — including the largest and the most awkward — rather than against a nominal figure.
Figure 3: The same parcel box design produced at three heights, the usual way a range covers different parcel sizes.
Use Cases: Which Size Suits Which Entrance
Single-House and Townhouse Entrances
A single-house entrance is the classic installation, and it is where parcel box dimensions are easiest to fix. The porch or wall beside the door usually allows a box around 400 to 550 mm wide and 500 to 800 mm tall, with a depth of 200 to 350 mm.
That depth is the number to argue about. A shallow box suits padded envelopes and small cartons and keeps the installation unobtrusive; a deeper box takes the shoebox-sized parcels that most online orders arrive in. On a single-house parcel box dimensions choice, the depth usually matters more than the width: 350 mm takes most parcel cartons, while 250 mm suits envelopes and thin boxes and keeps the installation visually lighter on a narrow wall.
Figure 4: A parcel box installed beside a residential front door, mounted at waist height.
Apartment and Multi-Unit Entrances
Apartment entrances change the brief. Several units share one wall, so the parcel box dimensions have to work in a row rather than alone: a narrow, tall module fits more households into the same run of wall than a wide, shallow one.
These installations also raise the retrieval question, because a shared entrance is not private. A box with a larger chamber but a narrow slot keeps the parcel out of reach of anyone passing, which is why apartment programmes often accept a deeper body in exchange for a more restricted opening. Consumer guidance on parcel theft and delivery practice is published by the US Postal Service.
Figure 5: Three parcel boxes in a row at an apartment entrance, sized to fit a shared wall.
Retail, Trade, and Commercial Deliveries
Trade and retail sites need a parcel box that takes bulkier items: sample cases, parts boxes, and multi-parcel deliveries. The parcel box dimensions here run larger in every direction, and the access door often becomes the primary opening, with the slot used as a secondary drop point.
These buyers also ask for a fixation that resists being leaned on or prised, and a lock that survives daily use by staff rather than occasional use by a homeowner. At this size the box is closer to a small cabinet than to a mailbox, and the sheet thickness steps up with it.
Slot Geometry and Anti-Theft Design
Slot Width, Height, and Angle
In any parcel box dimensions set, the slot is the smallest figure and the one that decides how much can be delivered. A slot of 300 x 40 mm takes padded envelopes and thin cartons; 350 x 60 mm takes most small parcels; anything larger starts to compromise the security the box exists to provide.
The angle matters as much as the size. A slot set at a downward angle, under a rain lip, forces the courier to push the parcel in and lets gravity carry it down to the flap. It also makes it far harder to reach in from outside, which is the whole point of the geometry.
The Retrieval Flap and What It Costs in Volume
Behind the slot sits a pivot flap that swings inward and then falls back under its own weight. That flap is what stops someone reaching down through the slot, and it is also what takes volume out of the chamber: the parcel has to push past it before it lands.
When a buyer settles parcel box dimensions, the flap has to be counted. A flap that needs 60 mm of clear swing reduces the usable height of the chamber by roughly that amount, so a box quoted as 300 mm deep internally may only accept a 240 mm parcel through the slot. The honest way to specify this is to state the largest parcel that will pass, not only the chamber volume.
Figure 6: The chamber with real parcels inside, showing how much of the volume the flap and baffle take up.
Keeping Small Parcels Out of Reach
A parcel that is small enough to pass back up through the slot is not secure, even inside a locked box. The usual answer is a horizontal baffle below the flap, positioned so that small items drop behind it while large ones cannot be lifted out.
That baffle is why parcel box dimensions cannot be optimised for volume alone. Every millimetre given to the security geometry is a millimetre taken from capacity, and the trade is decided by where the box is installed: an apartment entrance justifies more restriction than a porch in a quiet street.
Figure 7: The access door open, showing the opening that sets the largest parcel an owner can retrieve.
Production Difficulty and Quality Risks
From Parcel Size to Chamber Volume
The design sequence runs backwards from the parcel. The customer states the largest parcel that has to pass, the courier’s handling, and the wall space available; the factory then works out the slot, the flap clearance, the baffle position and, last, the outside size.
That order matters because a parcel box dimensions set derived from an external size is almost always either too small inside or heavier than it needs to be. The process control behind this translation is described by SME, and where a buyer has an existing box to replace, we measure it and issue a drawing for approval rather than scaling from the old product.
Tolerances That Decide Whether a Parcel Passes
On a parcel box dimensions set, the critical tolerances are the slot opening, the door opening and the flap clearances. A slot that is dimensioned correctly but formed 1.5 mm narrow will reject parcels that should have fitted, and the buyer will only find out from customers. Where an enclosure type or weathering expectation is specified, it is normally written against the standards published by NEMA.
Those features belong on the first article inspection report, measured rather than assumed, along with the door squareness. Thread and fastener standards for the lock and catch are published by ANSI, and dimensional verification follows the measurement practice published by NIST. A first article that lists the slot clear opening is more useful than one that lists only the outside box.
Figure 8: A parcel entering through the slot, the check that decides whether the slot dimensions are right.
Flatness, Sealing, and Door Alignment
A parcel box is welded and folded from thin sheet, so the door face can arrive slightly out of flat. On a parcel box dimensions set, that flatness matters as much as the slot size, because on an outdoor unit a twisted door shows up as a leak at one corner long before it leaks along the whole joint — the gasket cannot compress evenly.
The controls are a balanced weld sequence, a post-weld check against a straight edge, and a gasket carried in a formed channel rather than on a flat face. Coating follows the same discipline as any exterior metal product: one powder lot per order, recorded cure parameters and a retained sample, with the practice described by the Powder Coating Institute.
Lead Times, Files, and Order Flow
What You Send Us
To quote a custom size we need the largest parcel that must pass, the wall space available, the installation height, whether the box is exposed to rain, and the finish and lock you have in mind. If you already sell a box, send the sample and we will measure it.
Where the design is fixed, a STEP model or a dimensioned 2D drawing is ideal, with the slot, the door opening and the fixing pattern called out separately. For an outdoor parcel box dimensions set, state the expected exposure as well, because a coastal installation changes the material and coating rather than the geometry.
Batch Volumes, MOQ, and Realistic Pricing
A wall mounted parcel box is a mid-size fabricated item. Realistic production runs from 50 to 300 pieces per batch over three to six releases a year, with a minimum order around 20 to 50 pieces depending on the size and the finish, and FOB prices typically between $30 and $78 each.
Within that band the price is set by the sheet thickness, the size of the blank, the lock and the coating rather than by the shape alone, and larger parcel box dimensions raise the blank, the coating area and the packed carton together. A small painted box with a cam lock sits at the bottom; a deeper galvanised body with a keyed lock, a baffle and a rain hood sits at the top. First batches ship 15 to 30 days after drawing and sample approval.
Assembly, Post-Processing, and Documents
XHX Metal cuts, punches, forms, welds, deburrs and finishes the body, fits the flap, the baffle, the gasket, the lock and the fixing brackets, and packs the finished item. Coating and galvanising are carried out by audited partners, with pre-treatment and film thickness recorded against the batch.
An order is supported by the approved drawing with its revision number, material certificates, a first article inspection report that records the slot and door openings, batch inspection records, and a packing list. Buyers who need third-party verification of the kind offered by UL should agree the scope at quotation. Material and coating choices for exterior products are described by SSINA, the American Galvanizers Association and, for aluminium bodies, the Aluminum Association and European Aluminium, with coating chemistry for the European market covered by EU REACH.
Figure 9: The access door with its keyed lock, the hardware that completes a parcel box specification.
Case Studies: Parcel Box Programmes
Case 1: US Home Brand — One Size, One Colour
A US home brand wanted a single wall mounted parcel box for its own store, sized around the padded envelopes and small cartons its customers actually ordered, in one colour to keep the range simple.
The parcel box dimensions were set from a sample of real parcels rather than from a nominal size, and the chamber was drawn around the largest of them with the flap clearance included. We built the body in 1.5 mm steel with a channel gasket, a rain lip and a cam lock, finished in a textured charcoal powder coat. Production ran at 300 pieces per batch, four releases a year, with an MOQ of 50 and FOB prices from $32 to $55. The first batch shipped 22 days after approval, and annual value was approximately $48,000.
Case 2: European Apartment Programme — Deeper Chamber
An apartment developer needed a parcel box dimensions set for a shared entrance, where the wall run was limited and several units had to be served from the same row.
We kept the module narrow and increased the depth instead, so the boxes fitted the available wall as a run of three while the chamber still took a standard parcel. The security geometry was tightened at the same time: a narrower slot and a horizontal baffle, so that small items could not be lifted back out. Production ran at 150 pieces per batch, three releases a year, with an MOQ of 30 and FOB prices from $45 to $78. The first batch shipped 26 days after approval, and annual value was approximately $33,000.
Figure 10: The side profile of a parcel box, showing how depth is added without widening the wall footprint.
Case 3: Trade Counter — Custom Slot for Bulk Deliveries
A trade supplier needed a parcel box for deliveries of sample cases and parts boxes, where the access door rather than the slot would carry most of the use.
The parcel box dimensions were reworked around the door: the access opening was enlarged and fitted with a heavier lock, while the slot stayed small so that the unit could still accept a drop when the counter was closed. The body was produced in 2.0 mm steel with a welded frame and a powder coat matched to the customer’s brand colour. Production ran at 200 pieces per batch, three releases a year, with an MOQ of 50 and FOB prices from $38 to $62. The first batch shipped 24 days after approval, and annual value was approximately $36,000.
Summary and Next Steps
How to Choose a Parcel Box Size
Start from the largest parcel that has to pass, not the outside size. Add the flap and baffle clearance to get the chamber, make sure the access door opening is at least as large as the slot, and only then decide the external parcel box dimensions against the wall you have.
For a wider view of the product, the guide to custom sheet metal parcel boxes covers the materials, door and lock design and the production route, and the product range page lists the wider scope.
Why XHX Metal
XHX Metal produces parcel boxes to the buyer’s parcel box dimensions, from drawing to delivered parts: laser cutting on two 6kW fiber laser cutting machines to plus or minus 0.01 mm, CNC punching and bending, TIG and MIG welding, deburring, powder coating and galvanising through audited partners, and export packing.
The company has manufactured sheet metal enclosures for export customers from Dongguan since 2014, and holds ISO 9001:2015 certification with CE documentation and SGS records. Samples in 5 to 10 working days and first batches in 15 to 30 days are normal work.
How to Start Your Programme
Send the largest parcel that must fit, the wall space, the mounting height, the exposure, the finish and the lock you need, and the annual volume. We will propose a parcel box dimensions set, issue a drawing, and build a sample for approval before any batch is released.
Programmes are handled directly through the contact page.
FAQ: Parcel Box Dimensions
How do I know what parcel box dimensions I need? Measure the largest parcel you expect to receive, add 20 to 30 mm for the flap and baffle, and use that as the minimum chamber size.
Do the outside dimensions tell me the internal size? No. Wall thickness, the flap, the baffle and the door frame all take volume out of the chamber, so ask for the clear opening and the maximum parcel size.
Can I have a custom slot size? Yes. The slot width and height are set by the drawing, and both are recorded on the first article report.
What is the minimum order? MOQ is typically 20 to 50 pieces depending on size and finish, with batches released three to six times a year.
Which size suits an apartment entrance? A narrow, deeper module usually works better than a wide box, because several units have to fit the same wall.
How long does a sample take? A sample follows in 5 to 10 working days after drawing approval, and the first batch ships 15 to 30 days after approval.
