1. Royal Mail Rates Updated April 2026

    UK Paper Weight,Thickness & MailingCost Comparison Guide

    Master your mailing strategy with our definitive guide to GSM, microns, and Royal Mail 2026 postage rates.

    Optimise your print choices to balance a premium feel with cost-effective distribution — and save thousands on direct mail campaigns.

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    Paper weight guide

    Smarter Print

    Why Paper Specification Matters in 2026

    A critical financial decision, not just a tactile one.

    For 2026, UK businesses face rising postage costs and increased sustainability scrutiny. Understanding the relationship between GSM and Microns is the key to staying under Royal Mail "Large Letter" thresholds while maintaining a professional brand identity.

    By selecting a high-bulk paper that feels substantial but weighs less — or choosing a fold that keeps thickness under 5mm — you can save thousands on direct mail campaigns.

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    Reference Data

    GSM vs. Thickness vs. Capacity

    The following table correlates standard paper weights to their average physical thickness in microns (µm). Bulk factors vary between coated (silk/gloss) and uncoated stocks — two papers of the same GSM can feel very different in the hand.

    Weight (GSM)Thickness (Microns)Typical Product UseMax A4 Sheets (under 100g)
    80–90gsm100–110µmEconomy letterheads, copier paper, internal documents15–18 sheets
    100–120gsm120–140µmPremium stationery, business letterheads, formal reports12–14 sheets
    130–150gsm150–170µmHigh-quality flyers, brochure inner pages8–10 sheets
    170gsm~200µmLuxury flyers, thin brochure covers, heavy-duty menus6–7 sheets
    250gsm~280µmRetail tags, premium brochure covers, greeting cards4 sheets
    300–350gsm350–420µmBusiness cards, postcards, luxury folders1–2 sheets

    Postage Rates

    2026 Royal Mail Postage Rates

    Effective 7th April 2026

    Postage costs for 2026 have been adjusted to reflect economic changes. The key to cost-effective mailing is understanding the 100g weight limit and the 5mm thickness rule for Standard Letters.

    Exceeding either threshold bumps your item into a more expensive category regardless of size — costing significantly more per piece at scale.

    Royal Mail postage rates
    FormatWeight LimitDimensions (Max)1st Class2nd Class
    Standard Letter0–100g24cm × 16.5cm × 0.5cm£1.80£0.91
    Large Letter0–100g35.3cm × 25cm × 2.5cm£3.30£1.55
    Large Letter101–250g35.3cm × 25cm × 2.5cm£3.60£1.90
    Small Parcel0–2kg45cm × 35cm × 16cm£5.45£4.25

    A4 sheets must be folded into a DL or C5 envelope to qualify for Standard Letter pricing. Unfolded A4 sheets in a C4 envelope are automatically classified as Large Letters regardless of weight — one of the most common and costly mistakes in direct mail planning.

    The 5mm rule

    Watch Out For

    The 5mm Rule: How Thickness Can Double Your Costs

    A Standard Letter must be no thicker than 5mm — including the envelope and all inserts. This is where businesses most commonly get caught out and face unexpected cost increases on campaigns.

    5mm
    The Threshold
    At 4.9mm: £0.91 (2nd Class). At 5.1mm: £1.55. A 70% cost increase for just 0.2mm over the limit.
    2×
    The Folding Factor
    Folding a sheet doubles its thickness at the fold. A 12-page booklet on 170gsm often exceeds 5mm even at only 40g.
    !
    The Material Trap
    Uncoated papers feel premium but are loftier — they push mailings over 5mm faster than a compressed Silk or Gloss finish of the same GSM.

    Bulk Planning

    Bulk Weight Calculations for A4 Sheets

    Planning a larger distribution? Use these weight estimates for standard quantities of A4 paper (210mm × 297mm) to calculate your logistics and postage costs before committing to a print run.

    Paper Weight (GSM)100 Sheets500 Sheets1,000 Sheets
    90gsm0.56kg2.81kg5.62kg
    120gsm0.75kg3.74kg7.48kg
    150gsm0.94kg4.68kg9.36kg
    170gsm1.06kg5.30kg10.60kg
    350gsm2.18kg10.91kg21.82kg

    Print Responsibly

    Sustainability: Print a Tree with Every Order

    At Printlogik, high-quality print shouldn't come at the cost of the planet. Selecting the right paper weight is also an environmental decision — lighter paper requires less energy to produce and less fuel to transport, significantly reducing your campaign's carbon footprint.

    Through our Print a Tree reforestation initiative, we help UK businesses offset their environmental impact. Our team can advise on recycled stocks and eco-friendly finishes that fully comply with 2026 Royal Mail mailing standards.

    • Lighter stocks cut postage costs and fuel emissions simultaneously
    • Recycled stocks reduce demand for virgin pulp and forest pressure
    • FSC-certified paper ensures responsible sourcing at every stage
    • Vegetable-based inks reduce chemical pollutants and aid recyclability
    Learn more about our sustainability commitment
    Sustainable print

    Common Questions

    Frequently Asked Questions

    What is the difference between GSM and Microns? ›

    GSM stands for Grams per Square Metre and measures the weight and density of the paper. Microns (µm) measure the physical thickness. Some papers are high-bulk — thick but light. Others like Gloss are calendered (pressed) to be thin but heavy. The two don't always correlate directly, which is why both matter when planning a mailing.

    How many A4 sheets can I fit in a 1st class letter? ›

    Typically 15–18 sheets of 80gsm or 12–14 sheets of 100gsm will stay under the 100g limit. You must fold them into a C5 or DL envelope to avoid the Large Letter surcharge. Always check the final folded thickness is under 5mm before committing to a print run.

    Is A4 always a Large Letter? ›

    If you use a C4 envelope (which holds A4 unfolded), it is always classified as a Large Letter — even at just 10g. To qualify for Standard Letter rates the envelope must be no larger than 240mm × 165mm (C5). This is one of the most common and costly mistakes in direct mail planning.

    Does Printlogik check my artwork for mailing compliance? ›

    Yes. Our free human artwork check includes a review of your document dimensions. If your design might trigger higher postage costs — such as a size that won't fit a standard envelope — we'll flag it before printing. This service is included with every order at no extra cost.

    How do I calculate the weight of a custom-sized flyer? ›

    The formula is: (Length in metres × Width in metres) × GSM = weight of one sheet. For example, an A5 flyer (0.148m × 0.210m) at 300gsm weighs approximately 9.3 grams. Multiply by quantity to calculate total campaign weight for logistics planning.

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    Explore our full range of flyers, letterheads, business cards, booklets, and more — all with our free human artwork check included.

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    Have a specific mailing campaign in mind? Our team will advise on the right paper weight, format, and finish to keep you under budget and over threshold.

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