QR Codes on Postcards: How to Drive and Track Online Conversions from Direct Mail
QR codes have become one of the most powerful bridges between physical mail and digital commerce. Smartphone penetration in Western Europe exceeds 80%, and the habit of scanning QR codes has accelerated dramatically since 2020. For e-commerce brands using postcards, a well-implemented QR code turns a piece of physical mail into a tracked, attributable digital conversion — closing the measurement gap that has historically made direct mail hard to justify to data-driven marketing teams.
Sizing, placement, and design principles
A scannable QR code on a postcard must be at least 2.5 cm × 2.5 cm — smaller than this and camera autofocus struggles, particularly on older devices. The optimal size for a standard A6 postcard (105 × 148 mm) is 3–4 cm, printed with high contrast (black on white, never dark on dark or light on light). Place the QR code on the back of the card in the lower right or centre, away from the postal address area and never bleeding off the edge. Surround it with at least 5 mm of clear space on all sides. Add a short instruction above or below: "Scan to claim your offer" — do not assume customers know what to do. Avoid decorating the QR code with excessive branding overlays or unusual shapes; readability drops significantly and failed scans create friction.
Unique QR codes per campaign and per customer
The tracking value of QR codes comes from uniqueness. A single QR code shared across 1,000 postcards tells you that 47 people scanned it — but nothing else. A unique QR code per card tells you exactly which customer scanned, when they scanned, whether they converted, and the order value. This per-card uniqueness is how Mayday implements QR codes: every postcard receives a unique URL that identifies the campaign, the customer, and the send batch. This data flows into your campaign dashboard and gives you individual-level attribution — the same data quality you expect from email click tracking. For A/B testing postcard variants, unique codes per variant are essential to accurate split measurement.
Landing page design for postcard-driven traffic
The landing page a QR scan reaches must be optimised for the context: a customer who scanned a postcard is already aware of your brand and interested enough to pick up their phone. Do not send them to your homepage. The landing page should: pre-apply the promo code automatically, show the specific offer from the postcard prominently, load in under 3 seconds on mobile (the scan is always on mobile), and have a single clear path to the product or category. If the postcard offered 15% off summer clothing, the landing page should show summer clothing with the discount pre-applied. Any mismatch between the postcard offer and the landing page increases abandonment significantly. Consider a dedicated campaign URL (e.g. mayday.sh/offer/summer26) that routes to a campaign-specific page, maintaining clean tracking without exposing your infrastructure.
Measuring QR code performance
Track three metrics at the QR level: scan rate (scans ÷ cards sent), conversion rate (purchases ÷ scans), and revenue per card. Typical scan rates for e-commerce win-back postcards range from 3–8%. Conversion rate from scan to purchase typically runs 15–30% — significantly higher than email click-to-purchase because the customer who scanned is already intent-qualified. Segment your scan data by time of day and day of week — most postcard scans happen within 72 hours of delivery, and weekend mornings show a higher scan-to-purchase conversion. Use this data to optimise your postcard delivery timing. Low scan rates (below 2%) often indicate a QR code sizing or contrast problem, unclear instruction text, or a mismatch between the offer and the audience — diagnose before scaling.
QR codes and GDPR compliance
When a customer scans a QR code from a postcard, they are initiating a web session that you can track. This tracking falls under your standard cookie consent and privacy framework — the same as any other web session. You do not need separate consent to use the QR URL as an attribution mechanism, as it is functionally equivalent to a UTM parameter. However, if you are building personalised retargeting audiences from QR scan data (e.g. serving ads to customers who scanned but did not convert), you will need to ensure this is disclosed in your privacy policy and supported by appropriate consent. For most e-commerce brands, the core use case — attributing the conversion to the direct mail campaign — is straightforward and does not raise compliance concerns.
Every Mayday postcard includes a unique, tracked QR code — connect your store and start attributing revenue from direct mail.
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