Glossary
PiP (Pricing in Proportion)
Definition
Royal Mail's Pricing in Proportion system, where postage is set by an item's size and thickness as well as its weight. It sorts mail into format bands such as Letter, Large Letter and Small Parcel.
Also known as: Pricing in Proportion, PiP format, Royal Mail size-based pricing
Pricing in Proportion (PiP) has governed Royal Mail pricing since 2006. Rather than charging on weight alone, Royal Mail measures the length, width and thickness of each item and slots it into a format band. A thin, light item in the Letter band is cheaper to send than a bulkier item of the same weight that falls into Large Letter or Small Parcel.
The practical impact for sellers is that packaging shape can move an item from one price band to the next. A product that would qualify as a Large Letter in a slim, die-cut mailer may tip into the more expensive Small Parcel band if posted in a deeper box. Choosing packaging that keeps depth within the Large Letter 25mm limit is one of the most reliable ways to control postage on lightweight goods.
The main bands are Letter (max 240 x 165 x 5mm, up to 100g), Large Letter (max 353 x 250 x 25mm, up to 750g) and Small Parcel (up to 45 x 35 x 16cm, up to 2kg), with larger items priced as Medium Parcels. Always confirm current limits and prices on Royal Mail's own pages before committing packaging specs.
What to check
- Measure the packed item, not just the empty box; padding and tape add thickness.
- Keep depth under 25mm if you want to stay in the Large Letter band.
- Check the heaviest configuration you send, as weight also decides the band.
- Use a PiP gauge or slot template to test items against the thickness limits.
- Confirm current dimensions and prices on Royal Mail before finalising packaging.
Need help choosing the right spec?
Tell us what you're packing and your quantities — we'll recommend the right size, grade or material and price it for your order.
PiP (Pricing in Proportion) — FAQs
What are the main Royal Mail PiP formats?
Related pages
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