You’re busy. Whether you ship invoices, promo packs, or subscription boxes, Royal Mail postage rates can eat into your margins—fast. Here you’ll learn exactly which envelope size matches each postage band, so you spend pennies, not pounds.
Royal Mail Envelope Postage—Your Quick-Fire Cheat Sheet
| Postage Band | Max Size (mm) | Max Thickness | Max Weight | Typical Pakoro Envelope |
|---|---|---|---|---|
| Letter | 240 × 165 | 5 mm | 100 g | C6 · DL · C5 |
| Large Letter | 353 × 250 | 25 mm | 750 g | C4 |
| Small Parcel | 450 × 350 | 160 mm | 2 kg | Bubble Mailer · Book Wrap |
| Medium Parcel | 610 × 460 | 460 mm | 20 kg | Book Wrap · Carton |
Need it faster? Stay under the Letter limits, stick on a First-Class stamp, and you’re off for just 85 p.
1. Master the Four Royal Mail Size Bands
1.1 Letter—C5 Is Your Money-Saver
- Stay under: 240 mm × 165 mm, 5 mm thick, 100 g.
- Best fit: A C5 envelope (162 mm × 229 mm). It slides under the limits with a few millimetres to spare.
- Use it when: You’re mailing greeting cards, invoices, or any A5 leaflet.
- Cost check: First Class 85 p, Second Class 66 p.
1.2 Large Letter—C4 Keeps A4 Flat
- Stay under: 353 mm × 250 mm, 25 mm thick, 750 g.
- Best fit: A C4 envelope (229 mm × 324 mm). Your A4 brochures arrive crease-free.
- Typical rate: From 75 p (2nd Class ≤ 100 g) up to £4.80 (1st Class ≤ 750 g).
- Pro tip: Need every extra millimetre? Pakoro stocks 249 mm × 352 mm “max-out” mailers.
1.3 Small Parcel—When Depth Jumps to 160 mm
Perfect for hoodies, product samples, or a stack of catalogues.
- Limits: 450 mm × 350 mm × 160 mm, 2 kg.
- Packaging picks: Bubble mailers or book wraps. They add protection yet stay light.
1.4 Medium Parcel—Bulk Without the Freight Bill
Send giveaways, gift bundles, or multiple SKUs.
- Limits: 610 mm × 460 mm × 460 mm, 20 kg.
- Packaging picks: Rigid book wraps or double-wall cartons keep contents safe.
2. Rapid-Fire FAQs (Featured-Snippet Ready)
What’s the largest envelope for a standard First-Class stamp?
240 mm × 165 mm, 5 mm thick, 100 g. A C5 envelope hits the sweet spot.
When does a “letter” turn into a “large letter”?
The moment any side exceeds 240 mm × 165 mm, thickness tops 5 mm, or weight passes 100 g.
Cheapest UK postage rate right now?
Second Class Letter—66 p. Stay inside Letter limits using C6, DL, or C5.
Which envelopes need extra postage?
Anything bigger, fatter, or heavier than the Letter limits. Measure twice; pay once.
3. How to Slash Your Mailing Costs Today
- Measure every dimension. Thickness catches teams out more than length or width.
- Weigh with contents. Samples, inserts, and tape add up.
- Pick the lightest mailer that protects. Pakoro’s book wraps are 20 % lighter than standard board backs.
- Batch-test. Post one trial item per size band to verify real-world rates.
- Automate. Use a postage-scale and template—your team avoids guesswork.
4. Still Unsure? Let Pakoro Help
You don’t need to wrestle with size charts alone. Pakoro’s packaging engineers optimise mailers for hundreds of UK brands every week. Tell us your product weight and dimensions—we’ll recommend the exact envelope that locks you into the lowest Royal Mail band.
- Explore our full range at Pakoro.com
- Ready for a custom quote? Talk to our team—response within 12 hours.
Key Takeaway
Stay within the Letter band whenever possible. Every millimetre trimmed and every gram shaved can cut your postage bill by up to 70 %. With Pakoro’s size-smart envelopes, you mail more for less—starting today.
