Heavy is a band, not an opinion, and the published ladders make it unusually easy to answer this question precisely. Parcelforce's home page weight selector prices from 11.95 pounds up to 5kg, then 14.20 to 10kg, 17.95 to 20kg and 21.40 to 30kg. So a 15kg parcel falls in the 17.95 band and a 25kg parcel in the 21.40 band. Royal Mail's small parcel stops at 2kg entirely, which is why heavy senders leave its cheapest tier immediately.
The published ladder, band by band
Parcelforce publishes four bands on its home page weight selector: from 11.95 pounds up to 5kg, 14.20 pounds to 10kg, 17.95 pounds to 20kg and 21.40 pounds to 30kg. Read that ladder carefully and two things follow. A 15kg parcel is priced at the 20kg band, 17.95 pounds, not at some figure interpolated between 10 and 20. And a 25kg parcel is priced at the 30kg band, 21.40 pounds. Bands do not reward you for being under them, which is why splitting a 21kg consignment into two rarely helps and consolidating a 12kg and a 13kg one usually does.
Where the cheaper carriers stop
Royal Mail's Small Parcel band ends at 2kg and 45cm x 35cm x 16cm, priced at 3.95 pounds online. Past that its Medium Parcel applies, published from 6.25 pounds online and 6.95 pounds in a branch. Evri stops charging by size at 2kg and switches to weight alone, pricing the 2 to 5kg band at 6.59 pounds. So below 5kg there are genuinely cheap options; above it the field narrows quickly, and by 20kg the parcel networks that remain are pricing close to the Parcelforce ladder.
Dimensions can matter more than the scales
Every heavy service carries a maximum length and girth as well as a maximum weight, and exceeding either moves the parcel to a dearer product or out of the parcel network entirely. Volumetric weight applies on many heavy services too, so a large light item can be charged as though it were at the top of a band it never reaches on the scales. Measure the packed box, take the longest side and the girth, and check both against the service's limits before booking rather than discovering a surcharge afterwards.
When a heavy parcel should become a pallet
Somewhere around 30kg the parcel networks stop being the right product. Above that the published ladders end and consignments are quoted individually, and a quarter pallet frequently beats several heavy parcels on both price and handling risk. The crossover depends on shape as much as weight: a dense compact 35kg item may still travel as a parcel on some services, while a bulky 25kg one may be quoted as freight. If you are regularly sending at the top of the ladder, price both products rather than assuming.
Questions people ask about heavy parcel delivery uk
How much does a 25kg parcel cost to send in the UK?
Parcelforce publishes 21.40 pounds for its up to 30kg band on its home page weight selector, which is the band a 25kg parcel falls into.
What about a 15kg parcel?
It falls in Parcelforce's up to 20kg band, published at 17.95 pounds. Bands price at their ceiling, so being under the limit does not reduce the charge.
What is the heaviest a Royal Mail small parcel can be?
2kg, within 45cm x 35cm x 16cm, priced at 3.95 pounds bought online. Past that its Medium Parcel applies, published from 6.25 pounds online and 6.95 in a branch.
When should I use a pallet instead?
Generally above about 30kg, where the published parcel ladders end. A quarter pallet often beats several heavy parcels on price and on handling risk, though shape matters as much as weight.