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Worm castings buying guide: litres, weight and pack

Updated: October 2026

You have an amazon.co.uk tab open, and the title says 40 litres of worm castings while the weight cell says 1 kg. Those two figures cannot describe the same parcel. This worm castings buying guide is how the Products Compared editorial team reads a listing before we treat the title as what will arrive. It uses the ten listings in our [worm humus comparison](/hub/diy-supplies/worm-humus), with shelf prices saved on 16 October 2026. A qualifying purchase can earn us a commission at no extra cost to you. We did not run a laboratory test. You should leave knowing when a litre price is usable, and when a bucket photo is not a bucket.

You have an amazon.co.uk tab open, and the title says 40 litres of worm castings while the weight cell says 1 kg. Those two figures cannot describe the same parcel.

Our top picks

McMillan McMillan worm humus, 10 litres

Best overall

McMillan McMillan worm humus, 10 litres
5.8/10about £26.95
View offer
Invigortex Invigortex castings bucket, 3 litres

Alternative

Invigortex Invigortex castings bucket, 3 litres
6.7/10about £10.99
View offer
B2C B2C worm castings, 1.5 litres

Rank 3

B2C B2C worm castings, 1.5 litres
6.9/10about £9.89
View offer
On this page
  1. 1.Read the litres against the weight
  2. 2.Price per litre only after that check
  3. 3.Organic, PAS 100 and peat
  4. 4.Bucket, bag and short measure

Read the litres against the weight

Start with three cells, not the stars. The title volume, the unit count and the volume field should name one pack, and the weight should be plausible beside them. In this set the B2C 1.5 litre granules do that. The title, the 1500 millilitre unit count and the 1.5 litre volume agree, and 850 g is printed next to them, at £9.89. The Invigortex 40 litre title is £29.99, and the weight cell is 1 kg with a unit count of 1 litre. The B2C 100 litre title is £44.50, with a weight of 850 g and a volume cell of 360 litres. A moist 100 litre bag cannot weigh 850 g. Cinomania's liquid is £28.00 and prints no volume. If the cells clash, stop using the title litres.

Price per litre only after that check

A small title here sits between £7.14 and £10.99. Where the cells agree, that works out at about £3 to £7 per stated litre. The 1.5 litre B2C bag is £9.89, about £6.59 a litre. The Invigortex 3 litre bucket title is £10.99, about £3.66 a litre. McMillan's 10 litre powder is £26.95 and the litre cells agree, about £2.70 a litre. It is not a reason to ignore one rating and a larva sentence. Willy Worms listed 20 litres at £9.99 on 16 October 2026, about £0.50 a litre, screened at 5 mm then 3 mm. Titles near £0.45 to £1.05 per litre are the ones whose kilogram cells stop matching. When you need bulk at all, read worm castings versus compost.
McMillan McMillan worm humus, 10 litres

Testsieger

McMillan McMillan worm humus, 10 litres
5.8/10about £26.95
View offer

Organic, PAS 100 and peat

None of these ten listings prints a PAS 100 number or a Soil Association approved-input number. PAS 100:2018 is the BSI specification behind UK compost certification. You would expect a certificate reference, not the phrase 100% organic on its own. B2C puts that phrase in the title. Invigortex bullets say 100% organic. McMillan says natural. No scheme is named. Garden Organic's warning still fits: organic on a bag is often a loose word, and an approved input is a different purchase. T26 is the GOV.UK exemption for a household wormery, up to 6 tonnes a year. It does not certify a shop bag. The Royal Horticultural Society says its own retail is no new peat from 1 January 2026. That is not a statute that forces you to buy castings.

Bucket, bag and short measure

The three Invigortex bucket titles say a reusable lidded bucket. The seven review texts are shared across the 3, 10 and 20 litre bucket files, and the buyers who name a size name 20 litres and a bag. Section 11 of the Consumer Rights Act 2015 says goods must match their description. Ask the seller which parcel this ASIN sends before you count on the lid. The 1.5 litre B2C file has six review texts, and two describe a clear or unexpected bag and a quantity that did not look right. Stars come last. A 4.2 from 50 on the 40 litre title is the same review file as the 3 litre bag, and the weight cell still says 1 kg.

Common questions

How do I compare a 3 litre bag with a 20 litre bag?
Only after both packs agree with themselves. Divide the shelf price by the litres the cells share, not by the biggest number in the title. A 3 litre listing at £10.99 is about £3.66 a litre if the title, the volume and the unit count all say 3 litres. A 20 litre title at £20.99 is not about £1 a litre when the unit count says 1 litre. A specialist bag such as Willy Worms at £9.99 is the outside comparison, and delivery sits on top.
What if the weight says 1 kg and the title says 40 litres?
Treat the title volume as unreliable. Moist castings are heavy, and a kilogram can describe a small bag, not a 40 litre sack. In this set that clash is the Invigortex 40 litre listing at £29.99, where the unit count is also 1 litre. Do not turn that title into a bargain litre price, and do not let a Garden rank override the cell.
Does 100% organic mean Soil Association or PAS 100?
On these listings it means neither. It is title or bullet wording. PAS 100:2018 is a compost specification for an audited producer. A Soil Association approved input is a separate farm scheme. Neither number is printed here. T26, the household wormery exemption, is not a product certificate. If you need a scheme, you need its name on the pack, and this folder does not supply one.
The photo shows a bucket and a bag arrived. What does that mean?
The listing described a bucket and the review says a bag arrived, so the goods did not match the description. Section 11 of the Consumer Rights Act 2015 is the rule that covers that. In this set the Invigortex texts that name a size talk about a 20 litre order. That file is shared with the 3 litre and 10 litre bucket titles, so it is not a separate test of each size. Ask which parcel you will get before you rely on a lid.
Are small bags always worse value?
They cost more per litre when the litres are real, and that can still be the clearer buy. The 1.5 litre B2C bag is about £6.59 a litre at £9.89, which is dear next to a specialist 20 litre bag near £0.50. It is still easier to interpret than a 100 litre title at £44.50 whose weight cell says 850 g. Value starts when the cells describe one parcel.

Related pages

Best worm castings

Worm humus

Worm castings for houseplants: a thin share indoors

How to use worm castings without treating them as compost

Worm castings vs compost: a small share, not the fill

Sources

Public UK sources for this comparison. amazon.co.uk listings were read on 16 October 2026.

  1. RHS, worm composting (retrieved 16 October 2026)
  2. RHS, homemade fertilisers (retrieved 16 October 2026)
  3. RHS, houseplant growing media (retrieved 16 October 2026)
  4. GOV.UK, waste exemption T26 (retrieved 16 October 2026)
  5. GOV.UK, compost from waste resource framework (retrieved 16 October 2026)
  6. PAS 100:2018 via NBS (retrieved 16 October 2026)
  7. Consumer Rights Act 2015, section 11 (retrieved 16 October 2026)
  8. RHS, statement on peat (retrieved 16 October 2026)
  9. Gardenware, how to apply worm castings (retrieved 16 October 2026)