A plain white envelope is the cheapest way a card gets from your table to a buyer, and the barest thing you will ever ship. No box, no crinkle paper, no branded insert, no tissue. There is an envelope, a sleeved card, two pieces of cardboard and a stamp.
So whatever you want the buyer to keep has to be on the holder. The envelope goes in the recycling and the shims go in the bin; the sleeve or bag around the card is the only thing that stays, which makes it the only surface where branding survives and the only place a number can ride. Here are the limits you work inside.
What PWE and FCML actually mean
PWE is hobby shorthand for plain white envelope: a card, sleeved and usually sandwiched between two cardboard shims, taped inside an ordinary letter envelope.
FCML is First-Class Mail Letter, the USPS class that envelope rides in. Sellers on eBay and Whatnot say "FCML" the way they say "PWE": the letter lane, priced by weight and size rather than as a parcel. It is the only reason a $3 common can move at all, since a parcel label costs more than the card.
Which orders may go by letter differs by platform and the rules change, so read the current seller policy where you sell. If you sell live, the Whatnot sellers page covers how numbering fits a show night.
The limits, honestly
| Limit | Letter rate |
|---|---|
| Maximum length | 11-1/2 in |
| Maximum height | 6-1/8 in |
| Maximum thickness | 1/4 in |
| Maximum weight | 3.5 oz |
| Minimum size | 5 in x 3-1/2 in, 0.007 in thick |
| Shape | Rectangular, even thickness, bendable |
A #6-3/4 envelope is 3-5/8 in x 6-1/2 in and a #10 is 4-1/8 in x 9-1/2 in, so size is rarely your problem. Weight is not either: a modern card runs around 1.8 grams against a 99-gram ceiling.
The two that bind are thickness and shape. Run your own stack — a card is roughly 0.020 in, penny sleeve walls add about 0.002 in each, and two cereal-box-grade shims add roughly 0.020 in apiece. That lands near 0.07 in loaded, well under a quarter inch.
Now put a top loader in. A common 35pt loader measures roughly 0.075 in on the outside, so even shimmed you are under 1/4 in. Thickness is not what catches it. Rigidity is. Letter mail is meant to be bendable and evenly thick, so a rigid piece is non-machinable and carries a surcharge; sent underpaid it comes back for postage due or gets chewed by equipment built for paper. Plenty of sellers do it anyway — the rules did not change because it is common. Price it as what it is, or move that card to a parcel. Measure your own stock either way; shim thickness varies most.
There is no tracking, and a number does not change that
Say it before you build anything on top of it: a letter-rate PWE has no tracking number and no insurance. Nothing scans it.
Printing a serial on the holder inside does not create one. The number is your record, not the carrier's — it lives on your bench sheet and in your photos and does nothing to the mail stream. What it does do is make one shipment specific instead of general: which card, under which code, on which date. That is worth something in your own records and nothing at all to the postal system.
Where the number goes when there is no box
The only permanent surfaces in a PWE are the sleeve and, if you use one, the bag. The seal is a die-cut printed holographic foil label and it goes on the plastic of a holder — never on the card itself, and never on a holder headed to a grader.
On a penny sleeve. For a card with real money in it, do not seal the sleeve at all: sleeve it, load it, seal the loader, as the penny sleeve guide explains. Letter-lane cards are the low-dollar end, though, and there a fold over the sleeve's open 2-5/8 in top edge is the right move. Per-face landing is (1.77 - T) / 2; at a sleeve's 0.004 in edge that is 0.883 in on each face.
On a team bag. A 3-3/8 in x 4 in bag is the tidier target and costs almost nothing in thickness. One Standard seal laid vertically with its midpoint on the flap's free edge puts 0.885 in on the flap and 0.885 in on the body — the team bag guide has the rest, and the placement hub covers every other format.
Standard or Large. The Standard is 1.77 in x 0.75 in (44.96 x 19.05 mm). The Large is 2.5 in x 1 in (63.5 x 25.4 mm), and 2.5 in is the full width of a card — on a 2-5/8 in sleeve it runs nearly edge to edge, while on a 3-3/8 in bag it leaves roughly 0.44 in each side. Sleeves take the Standard; bags take either.
Duo. The Duo layout is two numbered halves on one label you cut apart. With no packing slip in the envelope, one half rides on the holder and the other stays on your bench sheet.
The label is thin: it is not what pushes a letter past a quarter inch, the holder is. Gauge one finished piece before committing a run.
Numbering a lane this cheap
On the builder you pick your own prefix plus a sequence from a start number you set, random codes, a batch code plus a number, or no number at all. For letter volume, batch code plus number usually earns its keep: the show date carries the context and the number does the counting. Within one order, no two seals share a number.
You can add a QR to the seal record — a page showing the design, the number and the date it was logged. It says nothing about the card. Your log lives at My Seals, and a single code can be pulled up here.
None of it matters if the number never gets written down. One line per shipment — order, serial, date — plus a photo of the sealed holder before it goes in the envelope. That helps document what was shipped, and it helps deter swaps and return fraud by making your side of a conversation specific. The return-fraud page shows what that log looks like when a buyer disputes what arrived.
What a seal will not do
- It can be peeled off and replaced. It is a printed foil label on plastic, and somebody patient with a fingernail can lift it and put a different one down.
- It says nothing about the card. The seal records a number, a design and a date — not what is inside, its condition, or who printed it.
- It has no standing with any marketplace or grading company. eBay, Whatnot and the graders run their own processes on their own rules, and a serial is not an input to any of them.
- It does not decide a return. If a buyer opens a case, the platform decides it. Your log is something you can hand over; what they do with it is their call.
- It does not add tracking. Worth repeating, because it is what people most hope it does.
What it costs
Standard seals are $6.00 per pack of 12. The smallest order is 60 seals at $30.00 — 50c each. Past that: 45c at 120, 40c at 600, 36c at 1,200, 33c at 2,400 and 30c at 4,200. Self-serve tops out at 10,008 and larger runs are quoted. Large seals are $9.00 per pack of 12, 60 minimum at $45.00 (75c each), then 10% off at 120, 20% at 600, 30% at 1,200 and 40% at 4,200, which brings a Large down to 45c.
Run it against a real month. Ship 200 letters, add a few spares for the crooked ones, and you are ordering 216 — eighteen packs, past the 120 rung at 45c, $97.20.
Be honest about the ratio. On a letter shipment the seal is a real share of the cost: at 50c it can run past the envelope, sleeve and shims combined, and at 30c it is still not free. Number where being specific later has value, and let a 40c common in a bulk clear-out go plain.
Common mistakes
- Sealing the card. Never. The label goes on plastic, not on cardboard and not on factory-sealed wax.
- A Large seal on a penny sleeve. It is as wide as the card. Use the Standard on sleeves.
- Sealing everything and logging nothing. An unlogged number is decoration; the line on the sheet is the product.
- Calling a numbered PWE a tracked one. It is not, and saying so to a buyer comes back on you.
Frequently asked questions
Can I ship a top loader in a PWE?
It fits on thickness — a 35pt loader is roughly 0.075 in against a 1/4 in limit — but it fails on shape. Letter mail is meant to be bendable and evenly thick, so a rigid piece is non-machinable and carries a surcharge, and sent with plain letter postage it can come back for postage due. If a card is worth a loader, it is usually worth pricing as a parcel.
Does a numbered seal give my PWE tracking?
No. A letter-rate PWE has no tracking number and no insurance, and a serial printed on the holder inside creates neither. The number is your own record — bench sheet, photos, seal log.
Should I number every letter I send?
Probably not. At 50c a seal on a $3 card the number costs more than it earns, and the rate only reaches 30c at real volume. Number what has value in being specific later — repacks, hits, show orders, anything with a series behind it — and let bulk clear-outs go plain.
A PWE strips a shipment down to an envelope and a stamp, so the holder is the only branding and the only number that survives the trip. Pick a design, put your own logo or artwork on it and set your prefix on the builder, or the Large builder for bags. Then write the number down before the envelope closes, because that line, not the foil, is the part worth anything later.
Serial Seal is an independent printer, not affiliated with, endorsed by or sponsored by USPS, eBay, Whatnot, TCGplayer, PSA, Beckett, CGC, SGC, Ultra Pro, BCW or any card manufacturer. Postal rules and marketplace policies change — check the current ones. Nothing here is legal advice.