Sending a large parcel goes wrong at the measuring stage far more often than at the choosing stage. Every published price in this record is a band, the bands are set on the outside of the packed box, and every carrier reserves the right to re-measure in its own depot and bill the difference. Two minutes with a tape measure before you book is worth more than any amount of comparing afterwards, because it decides which prices are even available to you.
The bands you are actually choosing between
Royal Mail publishes a Small Parcel to 45cm x 35cm x 16cm and 2kg from £3.95 online, and a Medium Parcel to 61cm x 46cm x 46cm and 20kg from £6.25 online. Evri publishes 0-1kg Small at £3.04 and 1-2kg Small at £3.52, then abandons the size split and prices 2-5kg at £6.59 on weight alone. For a bulky but light parcel, that second grid is often the cheaper one and it is not obvious from any headline.
Why one long side costs more than a few kilos
Most parcels that move up a band do so on a single dimension rather than on volume or weight. A 47cm box is a Medium Parcel to Royal Mail however light it is, and the item inside might be 40cm. Packing to the shortest honest box is the cheapest optimisation available to a sender, and it is entirely within your control in a way the carrier's rates are not.
What happens when you get it wrong
The carrier re-measures, re-bands and bills the difference, usually after delivery and usually with an administration charge on top. None of the four companies that publish a price in this record publishes what that surcharge is, which is a reason to measure rather than to estimate. It is also why the packed box is what matters: a carrier measures what arrives, not what you meant to send.
Sending several large parcels at once
Above three or four heavy boxes to one address, get a pallet quote beside the parcel prices. A pallet is priced per pallet by footprint and height rather than per kilogram, so the cost per box falls the fuller it is, and the crossover is often lower than people expect. Below that, parcels win because they are sold from a published price list and a pallet is not.
Questions people ask about send large parcel
How do I send a large parcel in the UK?
Measure the packed box first and check it against the published bands: Royal Mail's Medium Parcel takes 61cm x 46cm x 46cm and 20kg from £6.25 online, and Evri prices 2-5kg at £6.59 with no size split above 2kg.
What is the largest parcel I can send?
On the published grids, 61cm x 46cm x 46cm and 20kg with Royal Mail. Beyond that no company in this record publishes a price and the service is quoted.
Why did my large parcel cost more than the price I booked?
Almost always a re-measure in the depot. Carriers band on the outside of the packed box and bill the difference if it is bigger than declared.
Is it cheaper to send one large parcel or several small ones?
It depends which bands each lands in. Two Royal Mail Small Parcels at £3.95 online come to more than one Medium at £6.25, but two Evri 0-1kg Smalls at £3.04 come to less than one 2-5kg at £6.59.