Making a parcel mailbox yourself sounds like a Saturday project: some Douglas fir, a couple of hinges, a lock on it, and you're done. Until the first parcel comes that doesn't fit. Or does fit, but has to be fished out through the flap again. Size is more important than the wood in this project, and that's where this story begins.
How big should a parcel mailbox be?
PostNL works with a few fixed sizes, and those determine what your box needs to be able to swallow. A letterbox parcel is a maximum of 38 by 26.5 by 3.2 centimeters and weighs up to two kilos. A small parcel is a maximum of 34 by 28 by 15 centimeters and weighs up to three kilos. A standard parcel can measure up to 100 by 50 by 50 centimeters and weigh ten kilos, and at the very top is a limit of 178 by 78 by 58 centimeters and 23 kilos.
You won't be accommodating those last two in a self-built box next to the front door, and you don't need to. The majority of what is delivered to homes falls into the first two categories. Aim for an interior space of about 40 by 35 by 20 centimeters, and you'll accommodate letterbox parcels and small parcels. If you also want to fit medium-sized boxes, you're quickly talking about an interior size towards 50 by 44 by 37 centimeters, and that's no longer a box but a column.
Calculating the flap opening
The interior size is one thing, the opening the parcel has to go through is another. A box goes through with its two smallest sides, so that's what you look at. A small parcel of 34 by 28 by 15 centimeters goes through standing up through an opening of 28 by 15, and lying down through 34 by 15. Add two centimeters of clearance to both, because the delivery person doesn't push straight and the edges of a box are rarely flush.
That gives most households an opening of about 36 by 17 centimeters. Wider is fine, higher becomes difficult, because the higher the flap, the easier it is for an arm to go through. That's the trade-off you make: every extra centimeter of height in the opening makes the box more welcoming to parcels and fingers at the same time.
If you're somewhere in between, choose wider instead of higher. A wide, low slot lets flat boxes through perfectly and keeps the opening inaccessible, while a square hole of twenty by twenty is exactly the size that a hand with a hook fits through.
Start with your own orders, not a building plan
Most building plans you find online start with the wood the maker happened to have left over. Turn it around. Go through your order history from the past few months and see what came in. For some, that's mostly clothes and books, for others boxes of cat food or a new kettle. That difference determines whether you can get away with a flat box or need a tall one.
Then measure the largest box you've received in the past half year and add five centimeters to each side. The delivery person doesn't aim millimeter-precisely and wants to let the parcel drop in with one hand. A box that fits exactly on paper is in practice a box the delivery person will struggle with and give to the neighbors the next time.
Wood, thickness and what's left outside
Wood standing outside has it tough. Douglas fir and larch hold up well without treatment, spruce does not. Below eighteen millimeters thick, a panel of those dimensions becomes flimsy, and a flimsy wall means a door that no longer closes after half a year. Four centimeters thick is not necessary, because then you can no longer lift the box and you lose the interior space you just calculated.
Account for the wall thickness when sawing. Someone who wants an interior size of forty centimeters and works with eighteen millimeters saws the exterior size at over forty-three. That sounds obvious and is exactly where it often goes wrong with self-building: the drawing gives exterior dimensions, you calculate with interior dimensions, and the parcel just doesn't fit.
The flap is the hardest part
A box with a lid is easy to make. A box where a parcel can go in but not out is a completely different story. That is the principle that manufacturers call an anti-fishing system: after dropping it in, the parcel falls into a space that is no longer accessible from the flap, usually because there is a partition or a slanted bottom in between.
You build that yourself with a flap that does not open further than necessary and a slanted inner partition under the opening. The opening must be large enough for your largest size and too small for an arm with a hook. Those are two requirements that work against each other, and that's where many a self-build project runs aground. If you can't manage it, a box with just a lock is more honest: then you know that the contents are safe as long as it is closed, and you don't pretend it can do more.
Rain from above, moisture from below
The flap is the place where the water gets in. Let the roof overhang a bit and place the flap under a slope, so that rain runs off it instead of into it. A rubber strip along the edge makes more difference than an extra layer of paint.
From below, the problem is different. A wooden box standing on tiles or on the ground absorbs moisture and rots from the bottom up, even if the top stays dry. Put it on legs or on a few tiles with air underneath. Drill a few holes in the bottom, because condensation will get in one way or another, and that needs to go somewhere. A parcel that was delivered dry and comes out of the box wet is just as good as damage.
A loose box gets taken away
A wooden chest of twenty kilos seems heavy enough to stay standing. Full, it is too. Empty, one person lifts it up and walks away with it, and that is exactly the moment it disappears. Secure the box to the wall, or to the ground if there is no wall nearby, with bolts that are secured from the inside.
The same applies to the lock. A padlock on a wooden bracket is loose within a minute, because not the lock gives way but the wood around it. A cylinder lock that goes through a thick wall and grips behind a metal plate does hold up. Think about that in the design, not only when the box is already assembled.
The order in which you best build it
Start with the interior size you calculated in step one and draw around it, not the other way around. First saw the bottom and the two side walls, fix them at right angles and check with a thumb ruler if your largest box stands freely inside before you continue. This is the only moment when correcting is still cheap.
Then the back wall goes on, because that makes the whole thing rigid and determines whether the box stays straight. Only when the shell is correct do you measure the flap opening and saw the front panel. Someone who works the other way around and saws the front panel to size beforehand finds out during assembly that the box is a few millimeters out of plumb and that the flap jams.
You put the lock in before the lid is closed, not after, because you need to be able to reach it with two hands. Drill the mounting holes for the wall or the floor at the same stage, for the same reason. Staining or painting you do last and on all sides, also on the bottom and on the sawed surfaces, because that's where moisture enters first. Let the box really dry afterwards before it goes outside.
What it costs when you add it all up
The building plans usually calculate the wood and nothing else. Add the rest yourself: hinges that do not rust outside, a cylinder lock, bolts and plugs, a rubber strip, stain or paint, and the screws. Then comes the saw, the drill and your Saturday, and if you have the wood cut to size, that amount too.
What comes out differs greatly per design, so calculate it for your box instead of adopting a figure from a blog. The comparison that counts is not wood versus a ready-made safe, but your complete list versus a safe that comes out of the box already galvanized, coated and locked.
Where it stands and what the delivery person needs to be able to do
A parcel mailbox only works if the delivery person sees it standing and understands what to do with it. Put it in sight from the path to the front door, not behind the hedge or around the corner. No app, no code and no note with instructions, because a delivery person in a hurry does not read that and walks on to the neighbors.
Also keep in mind that a parcel that must be signed for usually does not stay in a safe, no matter how beautifully you build it. That is not a feature of your box but of the shipment. For everything that is delivered without a signature, it saves you the trip around the pickup point. If regular mail also comes in, then you also need a mailbox, or a model that contains both.
Mail and parcels in one cabinet
Anyone who is building anyway can immediately include regular mail in it. That saves a second cabinet on the facade and looks tidier. The layout that works is a narrow slot at the top for letters and letterbox parcels, and below that a spacious compartment with its own flap for the boxes.
Keep those two separated inside. If letters end up at the bottom among the parcels, you will fish them out every time and sooner or later something will get lost behind a box. An intermediate partition with its own bottom under the letter slot solves that and costs you one board.
Make the slot itself spacious enough for a letterbox parcel, so at least 27 centimeters wide and over three centimeters high. If you skimp on that, only envelopes fit and the parcels end up at the neighbors after all. A flap or a brush strip on the inside keeps rain and wind out, and that is no unnecessary luxury for a slot at eye level.
When a ready-made safe is more logical
Building yourself pays off if you already have the wood lying around, the tools are in the shed and you enjoy it. If one of those three does not work, it will be an expensive Saturday with a box that just doesn't close.
The parcel safes from Avalo solve exactly the two things that self-building runs aground on. The compact box of 44 by 22 by 82 centimeters accommodates parcels up to 39 by 30 by 13 centimeters and is closed with a cylinder lock. The two columns of 112 centimeters have a parcel compartment of 50 by 44 by 37 centimeters, a separate slot at the top for mail and letterbox parcels, and an anti-fishing system that closes automatically after dropping it in. All made of galvanized steel with powder coating, mounting material included, and no batteries, power or app needed. One version also has an LED strip under the flap that turns on with solar energy at dusk, so the delivery person sees where they need to be in the winter.
Frequently asked questions about making a parcel mailbox yourself
How big should a parcel mailbox be?
For letterbox parcels and small parcels, an interior space of about 40 by 35 by 20 centimeters is sufficient. A letterbox parcel is after all a maximum of 38 by 26.5 by 3.2 centimeters and a small parcel 34 by 28 by 15 centimeters. If you also want to accommodate medium-sized boxes, go towards 50 by 44 by 37 centimeters.
Is a regular mailbox also suitable for parcels?
Only for letterbox parcels, and even then not always. They are up to 3.2 centimeters thick, so anything thicker simply does not fit through. For parcels with volume, you need a safe or a column.
What wood is best to use?
Douglas fir or larch, because they hold up outside without you having to follow up every year. Work with panels of at least eighteen millimeters, otherwise the walls will move and the door will no longer close after a season.
How do I prevent someone from taking the parcel out again?
With a flap that does not open further than necessary and a partition or slanted bottom that drops the contents out of reach. If you can't manage that, choose a box that simply locks instead of an open drop-in flap.
Is making it yourself cheaper than buying a parcel safe?
That depends on what you already have in the house. Add up the wood, the hinges, the lock, the mounting material and the finish, and compare that with a safe that comes galvanized and coated out of the box. If you don't have the material and the tools lying around, the difference often disappoints.
