For most UK business post, an envelope between 90gsm and 120gsm is the right choice. Anything below about 80gsm feels flimsy and lets the contents show through, while anything much above 120gsm starts eating into your Royal Mail weight allowance without adding much real protection. The trick is to match the paper weight to what you are actually posting, then check how that weight behaves once it goes through a printer.
Below is a plain-English guide to envelope gsm: what the number means, which weights suit which jobs, and how paper weight quietly affects both your print quality and your postage.
What does gsm actually mean?
Gsm stands for grams per square metre. It measures how much a single square metre of that paper weighs, and is defined internationally by the ISO 536 standard for grammage. A sheet of A0 paper measures exactly one square metre, so an A0 sheet of 100gsm paper weighs 100 grams. There is a fuller technical explanation in the Paper Sizes guide to paper weights and ISO 536.
In everyday use, gsm is treated as a proxy for thickness and sturdiness. It is not a perfect one, because two papers at the same gsm can feel different depending on how bulky the fibres are and whether the surface is coated. As shorthand for how substantial an envelope feels, though, it is the number the whole industry uses.
For context, the copier paper in your office is usually 70gsm to 80gsm, with 80gsm by far the most common. Solicitors and accountants often move up to 90gsm or 120gsm for formal letters, and anything above 120gsm is generally described as card rather than paper.
Common envelope paper weights and what they suit
Envelope stock is typically manufactured somewhere between roughly 70gsm and 180gsm. Here is how the usual bands break down in practice:
- 70gsm to 80gsm - the budget end. Fine for very high volume, low value mailings where cost per unit is everything. Expect visible show-through and a noticeably lightweight feel in the hand.
- 90gsm - the everyday business standard. A good balance of opacity, cost and postal weight for letterheads, invoices and statements in DL and C5.
- 100gsm to 120gsm - the quality tier. Better opacity, a more confident feel, and a much better surface for printing on. Worth the step up for customer-facing post and branded mail.
- 120gsm and above - premium and protective territory. Common for larger C4 pocket envelopes carrying several sheets, and for invitations or documents where presentation matters.
A useful rule of thumb: the bigger the envelope, the higher the gsm needs to be. A C4 holding ten A4 sheets carries far more weight across a larger unsupported area than a DL with one folded letter, so a weight that feels solid in DL can feel floppy in C4. If you are still deciding on format, our guide to envelope sizes explained for C4, C5, C6 and DL covers which format fits what.
How gsm affects your printed result
This is the part most buyers overlook until they see a proof. We print full-colour CMYK water-based digital inkjet directly onto pre-manufactured stock envelopes, and paper weight affects how that ink behaves.
Lighter, more absorbent stock soaks up more ink, so colours can look slightly softer and fine detail can spread a little at the edges. Heavier, denser stock generally holds ink better and gives crisper edges and stronger colour. It is one reason a logo that looks razor sharp on 120gsm can look marginally softer on 80gsm.
Two things are worth knowing whatever weight you choose. First, there is no white ink in the process, so any white in your artwork simply shows as the bare colour of the envelope itself. On kraft or manila stock, that means "white" reads as brown. Second, large areas of solid block colour are best avoided at any gsm, because inkjet on uncoated stock tends to band and print patchily across big flood fills. Clean logos, outlined type and line work reproduce far better. Our guide to preparing print-ready artwork for printed envelopes goes through this in detail.
Printing sits inside a defined print area rather than running to the edges, and is kept clear of the seal. Depending on the product you can print the front side only, the rear side only, or front and rear sides. The exact printable area for your chosen size is shown on each product page.
How gsm affects your postage
Envelope weight is part of your total mailing weight, and in the UK that can decide which postal format you fall into. A Royal Mail Large Letter must be no more than 353mm x 250mm x 25mm and no heavier than 750g, as set out in the official Royal Mail size and weight guide. Cross any one of those limits and the whole item moves up a band.
For a single DL letter, the difference between 90gsm and 120gsm is a couple of grams and will almost never change your postage. For a heavy C4 mailing sitting near a price threshold, the envelope choice really can tip you over, so weigh a made-up sample before committing to a full run. Our article on how envelope size affects your Royal Mail postage explains where those thresholds bite.
When gsm is the wrong question
Gsm is a paper measurement, so it is the right question for flat paper envelopes such as self seal, gummed and folding inserting machine formats. It is much less useful for protective mailers. Padded envelopes are rated by their padding and construction rather than a single paper weight, and cardboard envelopes are described by board type, such as standard solid board or premium corrugated, because rigidity rather than grammage is what stops a print bending in transit. If protection matters more than presentation, look at the board or padding specification instead of chasing a higher gsm.
Choosing a weight with confidence
If you are unsure, do not guess from a number on a screen. Order a printed sample in the format and size you are considering, hold it up to the light, and put your own artwork on it. Feel and opacity are hard to judge from a product photo, and a sample costs a fraction of a full run.
Remember too that heavier is not automatically greener, since a higher gsm envelope uses more fibre per unit. If sustainability matters to you, weigh that against recyclability and material choice, which we cover in our guide to whether printed envelopes are recyclable.
Frequently asked questions
What gsm is a standard business envelope?
Most standard UK business envelopes sit at around 90gsm. That is the usual weight for everyday DL and C5 correspondence such as invoices, statements and letterheads. Stepping up to 100gsm or 120gsm gives better opacity and a more premium feel for customer-facing post.
Is a higher gsm envelope always better?
No. Higher gsm means more opacity and a sturdier feel, but also more weight and more cost per envelope. On a large mailing close to a Royal Mail price threshold, the extra grams can push you into a dearer band. Choose the lowest weight that still gives the opacity and feel you need.
What gsm stops the contents showing through?
Show-through depends on opacity as well as weight, but as a general guide 80gsm and below will often let dark print or coloured paper show through, while 100gsm and above rarely does. If you are posting anything confidential, choose a heavier weight and check a sample against a bright light before committing.
Does envelope gsm change the print quality?
Yes, though usually subtly. Lighter, more absorbent stock takes on more ink, softening colours and fine detail slightly, while heavier stock holds ink better and gives crisper edges. Whatever the weight, there is no white ink, so white in your artwork appears as the bare envelope colour, and large solid blocks of colour are best avoided because inkjet on stock can band.
What gsm should a C4 envelope be?
C4 envelopes are usually specified at 100gsm to 120gsm or higher. Because a C4 carries multiple A4 sheets across a larger unsupported area, a weight that feels solid in a small envelope can feel flimsy at C4 size and is more prone to tearing at the corners in transit.
Can I print on any envelope weight?
Within our stock range, yes. Printing sits inside a defined print area kept clear of the seal, and depending on the product you can print the front side, the rear side, or both. Weight affects how the ink sits rather than whether it can be printed at all.
Get your envelopes printed by Fast Printed Envelopes
Whether you need a workhorse 90gsm DL for daily invoicing or something heavier for post that needs to make an impression, we print full-colour branded envelopes with a proof before every run. Browse the range at Fast Printed Envelopes, or order a printed sample first so you can feel the weight for yourself before committing to a full order.