In short
- At 40 orders a month, 1.2 units per order and 10 days to replenish, the example batch is 48 + 16 = 64 units. That is a planning example, not a minimum. Send less if it will not fit or you cannot afford the stock risk.
- Two reasons to go smaller: you should be able to write the batch off, and it has to fit the storage on the sender’s card. Two reasons never to go bigger: it does not lower the cost per order, and it raises what is at risk in someone’s home.
- Send the second batch when stock reaches the lead-time level, not when it runs out. The app shows the count per sender; check it mid-month.
- The batch size does not change what you pay per order — about €3.10 plus the label for a small parcel, whether fifty units or five hundred sit on the shelf. There is no volume discount to chase.
- For a second country or a second sender in the same country, repeat the sum for that country’s orders. Do not split one country’s batch across two senders until you have run one for a month.
- AirPost is a peer-to-peer fulfilment network: online shops have their orders packed and dropped at a parcel point by verified people near their customers, who earn a fee per parcel from home. No warehouse, no minimum order volume.
Every article about fulfilment without a warehouse ends the same way: start with one product, one batch, about a month of orders. That is good advice and it hides a question. How many units is a month? And what if the top-up takes ten days — do you add those?
This article does the arithmetic. It is short, because the sum is short, and most of it is about the two constraints that should make you send less than the sum says.
How much stock should I send a sender for the first batch?
| Number | Where you find it | Example |
|---|---|---|
| Orders a month, in that country, for that product | Your last three months, averaged. Orders, not revenue | 40 |
| Units per order | Total units sold ÷ orders. Usually between 1 and 1.5 for a single product | 1.2 |
| Top-up lead time | Days from deciding to top up until the box is on the sender’s shelf. Include your own delay | 10 days |
A month of units
Orders a month × units per order. 40 × 1.2 = 48 units. That is what leaves the shelf in a normal month.
Add the lead time
The units that sell while a top-up is in transit: monthly units × lead days ÷ 30. 48 × 10 ÷ 30 ≈ 16 units. Without this you order the top-up on the day you run out and lose ten days of orders.
That is the batch
48 + 16 = 64 units. Round to whatever your supplier packs in — a carton of 50 or 60 is fine here.
Then check the two constraints below
If either says "smaller", go smaller. The sum is a ceiling, not a target.
Two reasons to send less
Can you write it off?
Stock in someone’s home is stock in someone’s home. Verification and stock records lower the odds of it going wrong; they do not insure it. Many business policies can add "stock at another location"; ask your insurer. The honest test: if this batch vanished tomorrow, would it hurt or would it end you? If the second, halve it and top up more often.
Does it fit the sender’s space?
A sender’s card says where they store — cupboard, room, shed, garage — with an estimate in cubic metres. Fifty letterbox parcels fit anywhere; fifty medium boxes do not fit a cupboard. Work out the volume of your batch as packed (units × the box you ship in) and compare. A sender who says yes to a batch that does not fit is a sender you will hear from in a week.
Bigger does not make it cheaper
Unlike a warehouse, there is no volume tier here. A small parcel costs about €3.10 in fulfilment whether the batch was fifty or five hundred. A bigger batch buys you fewer top-ups and nothing else, and it raises what is at risk. That is why the sum above is a ceiling.
Batch size by volume
| Orders a month | Units a month (×1.2) | Lead time (10 days) | First batch | Roughly |
|---|---|---|---|---|
| 10 | 12 | 4 | 16 | One carton |
| 25 | 30 | 10 | 40 | One or two cartons |
| 40 | 48 | 16 | 64 | Two cartons |
| 80 | 96 | 32 | 128 | A shelf — check the sender’s space |
| 150 | 180 | 60 | 240 | A room or shed; consider two senders |
When to send the second batch
Not when the shelf is empty. The moment to top up is when the count reaches the lead-time level — in the example, when about ten units are left. Then the top-up lands as the last units go out, and no order waits.
The app shows the count per sender and per product; the sender sees the same number. Look at it mid-month, and after the first month set a rough rule for yourself: "top up when it hits X". After two or three cycles you will know whether your monthly number was right, and the batch can grow or shrink to match.
The second batch is also the moment to change one thing if the first month showed a problem: a different box, an insert, a different default shipping method. One change per batch, or you will not know which one worked.
A second country, or a second sender
- Second country: repeat the sum with that country’s orders. It is a separate batch with its own lead time — and, from outside the EU, its own customs event. Do not ship it via the first country’s sender; that makes every parcel cross-border again.
- Second sender in the same country: only after a month with one. Then split the country’s monthly units between them, roughly by the share of orders each is likely to claim, and keep both above their lead-time level. How offers are shared between senders is in offering one order to several senders at once.
- Second product: its own sum, its own batch, possibly the same sender if the space allows. Add it after the first product has run a full cycle, not alongside it.
How the model works and what an order costs is on local fulfilment in Europe. What the first batch fits into — the whole sequence from account to delivered order — is in your first order without a warehouse, step by step. Why you should hold stock near customers at all, and where, is in where to hold stock in Europe.
Frequently asked questions
How do I calculate the first stock batch for a sender?
Multiply monthly orders by units per order, then add monthly units × replenishment days ÷ 30 and round up. Calculate each destination separately. For example, shipping from stock in Spain needs its own sales forecast and top-up route.
Which days count towards replenishment lead time?
Count purchasing or production, packing, transport and receiving the stock at the sender. Use working or calendar days consistently and allow for variable demand. Test the assumptions with a first order without a warehouse.
Is a bigger batch cheaper per order?
No. Fulfilment costs the same per parcel — about €3.10 plus the label for a small parcel — whether fifty or five hundred units are on the shelf. A bigger batch only saves top-ups and raises what is at risk.
How do I know the batch will fit?
The sender’s card shows their storage type and an estimate in cubic metres. Work out your batch’s packed volume and compare. Letterbox parcels fit anywhere; medium boxes need a room or shed.
Is my stock insured while a sender holds it?
No. Verification and stock records reduce the risk; they do not insure the goods. Size the batch so you could write it off, and ask your insurer whether your policy can cover stock at another location.
Should I split one country’s stock across two senders from the start?
No. Run one sender for a month first. Then split by the share of orders each is likely to claim, and keep both above their lead-time level.
Sources
A month of orders is the ceiling. The batch you could lose without flinching is the number.
Find a sender with room for your first batch
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