Choosing the right size and format for a direct-mail campaign isn’t just about looks — it affects cost, delivery, engagement and ultimately response. Below are practical guidelines that help you pick the best option for your objective, audience and budget.
Match format to objective
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Postcards (A6 / A5) — Ideal for quick reminders, event invites, open-day prompts or local offers. They’re inexpensive, easy to scan at a glance, and don’t require opening. Use A6 (105 × 148 mm) for short messages or A5 (148 × 210 mm) when you need more space.
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Personal letters (DL / C5 in envelopes) — Best for higher-trust, conversion-focused messaging: membership renewals, offers, apologies or formal notices. Letters folded into a DL envelope (99 × 210 mm) feel personal; C5 envelopes (162 × 229 mm) suit A5 inserts or folded A4.
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Brochures & booklets (A4 / A5 / A4 folded) — Use when you need to present rich information: product catalogues, prospectuses, detailed service guides. A4 gives room for imagery and long copy; A5 booklets balance information and cost.
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Multi-piece mail packs & welcome kits — Great for onboarding, enrolment or VIP invites: combine a letter, brochure, flyers and gift/coupon in a box or polywrap for a premium feel. These attract attention but cost more to produce and post.
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Square mail or non-standard shapes — High-impact, memorable and often opened more readily — but expect higher postage and handling costs. Use them for targeted VIP or retention pieces where higher spend is justified.
Think about postage & cost bands
Size, weight and thickness determine postage class and price. Small, lightweight items are cheaper to post at bulk rates; larger or non-machinable shapes can push you into higher bands or require special handling. Factor postage early in format selection — the cheapest format isn’t always the most cost-effective once response rate is considered.
Design & production considerations
Allow for print needs: include bleed (usually 3mm), keep critical content inside the safe area, and avoid placing essential copy across a fold. For envelopes, front-facing design and teaser copy on the outer can significantly lift open rates. If your format will be machine-enclosed, design to standard pack dimensions; if hand-assembled, you have more creative freedom but higher labour costs.
Accessibility, tracking & response mechanics
Make response simple: include a single, clear CTA — PURL, QR code, short URL or dedicated phone number — and ensure landing pages are mobile-optimised. For older or less digital audiences, keep reply-paid options or phone numbers prominent. Consider large type, high contrast and plain language where accessibility matters.
Test and measure
Run format A/B tests — postcard vs letter, A5 vs DL — to see what resonates with your audience. Measure per-piece cost against response and conversion to find the right balance of impact and ROI.
Sustainability
If sustainability is part of your brand promise, choose FSC paper, recycled stocks and minimal external packaging. These choices can influence recipient perception without necessarily pushing costs too high.
How Herald Chase can help
If you’d like help matching format to objective, postage modelling or a sample pack to check finishes and sizes, book a free campaign review with our team at www.heraldchase.com — we’ll map the formats, costs and expected response so you can decide with confidence.
