Graded by quotient
Rank the tiers on one number only: pounds paid per kilogram of chargeable weight, with the first-kilogram fee divided across the whole parcel. Split routes score worse because they pay two first-kilogram fees for one delivery, and that single structural fact decides most of the ranking before any rate card is read.
1. Note the first-kilogram fee and the per-kilogram increment for your line. 2. Divide the total fee by the chargeable weight in kilograms. 3. Rank the tiers by that figure, not by the total you hand over, because a large parcel always costs more in total and that tells you nothing.
Score each split on three axes before trusting the ranking: 45% weight efficiency, 30% settlement drift against the quoted figure and 25% handling risk, then read the result against three bands — under £5.50/kg is worth merging, £5.50 to £7.00/kg is neutral and above £7.00/kg means the carton is carrying air — with boundaries at 1, 2, 3, 5, 8 and 10 kg across our 6 lanes × 9 bands. 1. Take the greater of actual and volumetric weight, rounding volumetric up to 0.5 kg, and divide freight by that figure rather than by the weight a seller declares. 2. Re-check the same lane twice inside a 12-snapshot window, since 4 of our re-checks showed a first-weight rise of up to +£1.60. On our £120 self-purchased parcel, 3.8 kg chargeable against £20.00 freight gave £5.26/kg, Recorded. Weight logged without a stated divisor stays Not verified.
One kilogram solo
One kilogram chargeable is the cheapest tier in the whole ranking at £8.40, which is £8.40 per kilogram, and splitting it is arithmetically impossible anyway because there is nothing to move out. The only lever at this tier is the volumetric minimum, where a 1.0 kg item in a 40 by 30 by 18 cm carton measures 3.6 kg and bills at 4.0 kg instead.
1. Weigh the item alone before you look at the carton. 2. Compute the volumetric figure for the carton you intend to use. 3. If volume drives the bill, fold or re-box rather than splitting, since a split at this weight doubles the first-kilogram fee for no gain.
Enter the single-parcel baseline first, because one box alone sets the floor that any split must beat. Our band structure opens at £8.40 first weight and steps in blocks — 2 kg = £13.20, 3 kg = £19.60, 3.8 kg = £26.40, 6 kg = £34.80, 10 kg = £54.60 — all Recorded from the 6-lane × 9-band sheet. 1. Work out cost per kilo at each 0.5 kg step and circle the plateaus, where two weights settle at one price: 8 kg and 8.5 kg both come to £43.60, and 10 kg and 11.5 kg both come to £54.60, so weight added inside a plateau is free until the next boundary. 2. Compare a lone 3.8 kg parcel at £26.40, which is £6.95/kg, against the same lane carrying 6 kg at £5.80/kg. If a parcel sits just under 3, 5 or 8 kg, top it up rather than splitting, and treat 14 kg and above on the identical band structure.
Pair, then trio
Two kilograms bills at £13.20, or £6.60 per kilogram, which is 21% cheaper per kilogram than tier 1 and beats any split you can construct at this weight. Two parcels of 1.0 kg each would cost £16.80, so the split loses £3.60 before the second tracking number is even printed.
The crossover arrives later than people expect. On our figures a single parcel stops being the cheaper option once the chargeable weight passes 3.0 kg and one component inside it can travel alone below 1.0 kg, because that component then escapes a per-kilogram increment entirely.
Compare a six-piece bundle against its divisors before merging anything, because volumetric weight ignores how light the contents are. 1. Measure the packed carton at its widest points rather than the flat item, then divide length × width × height by whichever divisor the lane states. 2. Round that answer up to 0.5 kg and keep the larger of it and the scale reading, so one 40 × 30 × 25 cm carton at 30,000 cubic centimetres becomes 6.0 kg at divisor 5000, 5.0 kg at 6000 and 4.0 kg at 8000. Those three answers span £8.40 on our table, since 6 kg settles at £34.80, Recorded, while the 3 to 5 kg band sits at £26.40, which is why 3 of 12 rate snapshots are logged as Not verified. If the merged volumetric weight reaches 14 kg, as a 50 × 40 × 35 cm carton does at divisor 5000, the quote follows the same band structure as 10 kg and splitting wins again.
Split at the plateau edges and treat every extra carton as a fresh cost line. Each additional box repeats packaging at £3.50 and its own domestic leg of ¥12 plus ¥8, both Recorded on our £120 parcel, so a six-way split adds five extra packaging charges. 1. Rank the six items by chargeable kilos per pound of goods value, and pull out only the heaviest while the remainder still clears a boundary at 5, 8 or 10 kg. 2. Re-check storage, because the free window runs from the inbound scan and overdue holding is Community-reported at £0.20 per item per day, with 8 of our 24 items running 1 to 14 days over and the longest bill near £2.80. If two light items together push volumetric weight past 8.5 kg, hold them back, since the £43.60 rate already covers 8 kg through 8.5 kg while stepping to 10 kg costs £11.00 more.
Half-a-dozen, the snag
Six kilograms bills at £34.80, which is £5.80 per kilogram, and a split into 2.0 kg and 4.0 kg bills at £13.20 plus £24.60, a total of £37.80. The split loses £3.00 on fees alone, so the tier ranking says ship it whole until the merged parcel crosses a band edge or the volumetric row differs between the two halves.
1. Compute the volumetric figure for the whole carton and for both halves. 2. Add the two half fees and compare against the single fee at the same divisor. 3. Split only where the two halves each stay under 5.0 kg chargeable and the total of the two fees is below the single fee, which on our rate snapshot happened on 2 of 6 lines.
Treat every rank as provisional until you re-run the settlement maths, because thin samples hold the top places. Route medians run from 8 days on a 4-parcel lane to 19 days on a 3-parcel lane, both Recorded across 24 UK parcels in the 2026-08-01 to 2026-09-30 window. 1. Downgrade any quality score built on flags: of 23 flags across 85 curated entries, 11 were labels, 6 were edge or border marks and 5 of those were lighting artefacts, leaving 4 hardware and 2 stitching cases with real defects. 2. Check reply latency before trusting a re-shoot record, since requests with explicit wording came back in 6 hours while vague ones took 2 days. Two coupon codes were refused inside the window for reasons we could not establish, so those rows stay Not verified until the settlement arithmetic is re-run on the whole list.
Octet lopsided
Eight kilograms bills at £43.60, or £5.45 per kilogram, the best ratio in the ranking. Splitting into 4.0 kg and 4.0 kg costs £24.60 twice, a total of £49.20, which loses £5.60. But where the two halves have very different densities the ranking flips: our 6.8 kg carton at 46 by 34 by 22 cm measured 6.0 kg volumetric, and moving the bulky component into its own smaller carton changed the volumetric figure from 6.0 kg to 4.5 kg on the same scale weight.
1. Measure both halves in their own cartons rather than dividing the parent measurements. 2. Recompute the volumetric figure for each half at the line divisor. 3. Compare the sum of the two chargeable figures against the parent chargeable figure, and split only when the sum is lower by 0.5 kg or more.
Ten inverted
Above 10.0 kg the per-kilogram figure keeps improving but the tail risk grows faster, because one damaged or delayed parcel now contains everything. Our heaviest recorded parcel billed at £54.60 for 10.0 kg, or £5.46 per kilogram, and the same goods split into 5.0 kg and 5.0 kg would have cost £31.80 twice, a total of £63.60 and a loss of £9.00.
Rank the tiers by cost per kilogram and then apply one override: never put more value in a single parcel than you would be willing to lose for six weeks. That override is why the 10.0 kg row, despite winning the ranking, is not automatically the answer.
Ranking beguiles
The ranking assumes every tier is available to you and that both halves of a split travel on the same line at the same rate, and neither assumption holds in three cases. Some lines refuse parcels above 5.0 kg for certain categories, so the higher tiers are not on the menu at all. A split creates two insurance positions and therefore two excess charges, which the fee arithmetic ignores. And a split parcel that arrives a week later than the whole one can miss a season, which no per-kilogram figure captures.
Use the ranking to find the two cheapest structures, then price the non-fee costs against them. On our record the split decision was right on 3 of 9 parcels where it was considered, and the reason it lost on the other 6 was a first-kilogram fee of £8.40 paid twice rather than any difference in rate cards.
The data point behind this note
On the recorded band table from 6 lines, a 6.0 kg parcel billed at £34.80 while the same goods split into 2.0 kg and 4.0 kg billed at £13.20 plus £24.60, a £3.00 loss driven by paying the first-kilogram fee twice (Recorded).
Rates last checked 2026-10-02. Where a figure is community-reported we say so; where we could not verify it, we write Not verified instead of estimating.