You already know postage adds up fast. Yet, every week, businesses overspend because envelopes are just a little too large, too thick, or too heavy. With this guide, you’ll:
- Match paper to envelope in seconds.
- Cut mailing costs by avoiding “non-machinable” surcharges.
- Elevate your brand with the right fit instead of a crumpled fold.
Ready? Let’s dive in.
Quick-Hit Envelope Size Cheat Sheet
| Envelope | Inside Dimensions (mm) | Fits Perfectly |
|---|---|---|
| DL | 110 × 220 | A4 folded twice (thirds) • Compliment slips |
| C6 | 114 × 162 | A6 postcards • A4 quarter-fold letters |
| C5 | 162 × 229 | A5 sheets • A4 half-fold brochures |
| C4 | 229 × 324 | Flat A4 documents • Contracts |
| C3 | 324 × 458 | Flat A3 plans • Large catalogues |
Bookmark this table. It slashes guess-work when the post room clock is ticking.
DL Envelope Size Explained
Core keyword: DL envelope size
A DL envelope measures 110 mm × 220 mm. Use it when you fold an A4 sheet twice, lengthwise. Because the profile is slim, your letter sails through automated sorting, and you pay the lowest standard letter rate.
When to choose DL
- Invoices and statements
- “With Compliments” slips (210 mm × 99 mm)
- Tri-fold sales letters that need to feel personal
Pro tip: If your pack includes a small card or extra flyer, jump to DL+ (114 mm × 229 mm) for extra breathing room without moving up a postage class.
C6 Envelope: Small Yet Mighty
Core keyword: C6 envelope
At 114 mm × 162 mm, the C6 envelope is the darling of greetings and promo mailers. Drop an A6 postcard inside and the edges stay pristine. Or, quarter-fold an A4 fact sheet and slide it in—no extra trimming needed.
Perfect for:
- Event invitations
- Thank-you notes with discount codes
- Loyalty cards that deserve a tactile touch
C5 Envelope: Half-Fold Hero
Core keyword: C5 envelope size
Need to mail an A4 brochure but hate awkward creases? Fold the sheet once and invite it into a C5 envelope (162 mm × 229 mm). The proportions feel premium, yet you still sit inside “large letter” pricing.
Use cases:
- Product catalogues up to 10 pages
- Interview packs and CVs
- Certificates that must avoid heavy folds
C4 Envelope: Keep A4 Flat, Keep Costs Flat
Core keyword: C4 envelope
When presentation is everything, never fold. A C4 envelope (229 mm × 324 mm) protects a full A4 document—proposals, legal forms, CAD drawings—without wrinkles. That polished look tells your client, “We care about every detail.”
Wallet vs Pocket
- Wallet (long-edge flap): Ideal when you insert multiple sheets quickly.
- Pocket (short-edge flap): Better security; contents slide deep so nothing peeks out.
C3 Envelope: Think Big, Ship Smart
Core keyword: C3 envelope
Blueprints, posters, oversized contracts—anything A3 should travel in C3 (324 mm × 458 mm). Because the format still fits within Royal Mail’s Packet category, you avoid tube surcharges and keep documents flat for instant board-room impact.
The “Swap A for C” Memory Hack
Still unsure? Replace the A in your paper size with a C and you’ve nailed the envelope size:
- A4 → C4
- A5 → C5
- A6 → C6
Yes, it’s that simple.
FAQ—Answering Your Top 5 Questions
- “Why does C5 look smaller than C4?”
The number shows how many times the base A0 sheet is folded. More folds mean a smaller size. - “What if my A4 brochure is chunky?”
Jump up one size or switch to a gusseted C4 to absorb the spine thickness. - “Is DL short for ‘Dimension Lengthwise’?”
Correct. The name dates back to German DIN standards. - “How do I stop self-seal flaps popping open?”
Press firmly for three seconds, then let envelopes cure flat for 20 minutes before stacking. - “Can I print full-bleed art on coloured envelopes?”
Absolutely. Pakoro’s digital presses handle short runs with razor-sharp registration.
Seal Types That Save Headaches
- Peel-and-Seal: Fast, clean, perfect for e-commerce pick-packs.
- Self-Seal: Two latex strips—press, hold, done.
- Gummed: Best for high-speed inserting machines and ultra-long shelf life.
Match the seal to your fulfilment workflow and watch efficiency climb.
Postage Maths: Avoid the “Non-Machinable” Trap
Royal Mail charges extra when your envelope exceeds 5 mm thickness or feels rigid. Therefore:
- Test-pack the fattest item you plan to mail.
- Slide it through a 5 mm slot gauge.
- If it jams, size up to a gusseted option before it hits the hundreds-per-month cost spiral.
Bulk Buying Made Easy with Pakoro
Need 5,000 C4 wallets in brand colours? Or a mixed pallet of DL, C5, and C6 ready for year-round campaigns? Pakoro has you covered:
- Rapid lead-times: Die-cut, print, and ship in as little as seven days.
- Eco options: FSC kraft, recycled white, or carbon-neutral bamboo.
- Tiered pricing: The more you buy, the lower your per-unit cost.
Browse the full range at Pakoro.com. Custom spec in mind? Jump straight to our team via Contact Us—we reply within four hours, every business day.
Your Next Step
Stop folding, over-paying, and guessing. Download Pakoro’s printable Envelope Size Guide, pin it above the printer, and order envelopes that fit first time—every time. Your documents (and your finance team) will thank you.
Ready to mail smarter? Visit Pakoro.com now, choose your perfect size, and experience packaging that delivers.
