Water Butt Sizes UK: Capacity and Dimensions, Measured

Water butt sizes at a glance: 100 to 1,000 litres

UK water butts run from slimline 100-litre models, about 32 to 36cm wide,³⁶ to 350-litre barrels.⁹ With room to spare, an IBC (the industrial container kind) holds 1,000 litres.¹¹ A standard water butt holds about 200 to 250 litres: the RHS works on 240¹ and the RSPB says over 200.² A 227-litre Harcostar kit is about 60 x 60 x 129cm.⁸

Everything in the chart is a real product, not an average. Height is the slippery figure: some listings measure with the stand, some without. Where a maker gives two heights for what looks like the same butt, you get both.

A dash means the listing we read didn’t give that figure. Strata’s range table leaves the second width blank for its 120-litre and 210-litre butts, so they get one width each.³

Standard water butt size? About 200 to 250 litres

There’s no official standard size. The RHS measures in 240-litre butts¹ and the RSPB says a standard butt holds over 200 litres.² Water Butts Direct, a specialist shop, says the sizes it sells most are the Harcostar 227L, the 350L Magnum and the Harcostar 168L.¹² So in practice a standard butt means about 200 to 250 litres. The round 227-litre Harcostar is 60cm across.⁸

Water Butts Direct sorts its range into small (50 to 150 litres), medium (160 to 245), large (250 to 550) and extra large above that.¹² Those are its own shop filters, not an industry rule, though the chart’s products fit them.

Measure the width first: it decides what fits

Width is usually the deciding figure. Where space is tight, the RHS points you to slimline and decorative models.¹ The widths below are the tank alone. A stand is optional, and some butts, like the 350-litre Magnum, are built to sit without one.⁹ If you use a stand, check its footprint too, using the stand figures under this list.

• Narrow side passage: tank only, Strata’s 100-litre slimline needs 32cm of width and 36cm of depth.³ Water Butts Direct’s 100-litre butt is 36cm square.⁶
• Against a house wall: tank only, the 250-litre slimline is 50cm wide and 54cm deep.⁴ That’s two and a half times the water of the 100-litre version for 18cm more width.^M
• Open corner or greenhouse end: a round barrel needs its full diameter clear. That’s 58cm for the 168-litre Harcostar⁷ and 780mm for the 350-litre Magnum.⁹
• IBC tank: 1,200mm by 1,000mm on the Sotralentz sheet,¹¹ so 1.2 square metres of ground before you leave room to get at the tap.^M

Strata stands. Strata lists stands separately from tanks. Its range table gives the slim stand, for the 100-litre and Amesbury butts, as 30.5cm high and 38.5cm long. The stand for the 210-litre and 250-litre butts is 32cm high and 55cm long. Both times the width is left blank.³ So length is the only footprint figure you get: 38.5cm of stand under a 36cm tank, and 55cm under a 54cm tank. Measure the stand itself before you commit to a tight gap.

An IBC is an industrial container, not a garden product. Its maker’s data sheet says don’t store it outside or in UV light for long periods.¹¹ That’s written about storage, but it’s a fair reason to shade or cover one you use as a rain tank.

Water butt height: add the stand

Most butts sit on a stand or bricks so a watering can fits under the tap.¹ That stand changes how high up the downpipe you need to be. The 168-litre Harcostar is 82cm on its own plus a 30cm stand, about 112cm together.⁷ Water Butts Direct lists its 100-litre butt at 92cm, and its staff put it at 121cm on the stand.⁶ Strata gives 32cm for the stand under its 210-litre and 250-litre butts, and 30.5cm for the slim stand under the 100-litre and Amesbury.³

The 350-litre Magnum works differently. Harcostar says it needs no stand and has two tap positions, one for a hose and one for filling a can.⁹ Its height is 1,200mm on the maker’s sheet⁹ but 108cm on a retailer listing,¹⁰ so measure the one you get before you cut anything.

Height matters because it sets where you cut the downpipe. Water Butts Direct says set the diverter level with the top of the butt so it doesn’t overflow.⁸ The RSPB says cut the downpipe just below the top of the butt.² Both diverter kits we checked fit standard 68mm round and 65mm square plastic downpipes. The 100-litre kit isn’t suitable for cast iron.⁶⁵

How heavy is a full water butt? About 1kg a litre

Water weighs roughly 1 gram per millilitre,¹⁵ so call it 1kg a litre. A full 227-litre kit then comes to about 235kg once you add its 7.7kg empty weight,^8M and a full 100-litre kit about 106kg.^6M A brimful 1,000-litre IBC holds 1,050 litres and weighs 62 to 69kg empty,¹¹ so it’s around 1.1 tonnes full.^M The RHS says stand butts on firm, level stands or bricks.¹

Linking butts: twice the water, twice the wall

The RHS suggests joining butts with connector kits or siphons,¹ and says linking slimlines is a way to store more where space is short.¹ Our sums from the chart widths, for butts standing side by side, touching:

• Two 227-litre Harcostar kits: 454 litres across about 120cm of wall.^M
• Two 100-litre slimlines: 200 litres in 64cm (Strata) to 72cm (Water Butts Direct).^M
• Three 250-litre slimlines: 750 litres across 150cm.^M

Linking doesn’t let you skip the diverter. A Water Butts Direct adviser points out the catch. Once it’s full, a butt with no diverter overflows, even when it’s linked to a second one.⁸

How fast a roof fills them: faster in winter

One millimetre of rain on one square metre of roof is one litre. Our water butt calculator multiplies roof area by yearly rainfall, then by 0.8. That 0.8 is a modelling allowance for water that never reaches the butt, not a measured figure for every roof.^M The table uses our own 30-year averages (1991 to 2020), worked out from the Met Office HadUK rainfall series.¹³ The Met Office doesn’t publish them in this form.

Two worked examples, both our sums. A 3m x 2m shed roof (6m²) in East Anglia, at 626.9mm, gives about 3,009 litres a year. Use the southern England figure of 808.0mm and it’s about 3,878 litres.^13M The RHS puts a small shed roof in dry south-east England at 2,500 to 3,500 litres a year. That’s enough for 10 to 15 standard 240-litre butts.¹ Our East Anglia figure falls inside that range, and the southern England one runs a little above it. The RHS doesn’t give the roof size it had in mind, so treat this as a rough sense check, not a match.

Summer’s slower. Southern England’s average June rainfall for 1991–2020 is 59.1mm,¹³ so a 20m² roof collects about 946 litres in an average June. That’s a little over four 227-litre butts.^M An average month isn’t a promise, and dry spells happen inside it. The RSPB notes butts fill fast over the winter months.²

For your own roof, use the calculator to work out what size you need for your roof.

M — GardenCalc’s own arithmetic, not an external source. Checked 1 October 2026. Rainfall averages are the mean of the Met Office “ann” column for 1991 to 2020 in each HadUK series file. Roof yield = roof area (m²) x rainfall (mm) x 0.8, the allowance used by the GardenCalc water butt calculator. Linked footprints = number of butts x the width in the chart. Full weight = capacity in litres x 1kg plus the listed empty weight.

Before you buy: three checks

• Get one with a close-fitting lid. The RHS says it keeps out rain-borne disease spores and discourages algae.¹
• Use butt water on established plants, not seedlings. The RHS says seedlings risk damping-off diseases.¹
• Clean it out once a year. The RHS says use warm water and a little washing-up liquid.¹

On licences, the Environment Agency covers England: water that’s only harvested rainwater needs no abstraction licence.¹⁴ The RHS says collecting rain off your roof is legal across the UK.¹

Frequently asked questions

Plan the rest of the set-up

Sources and checking notes

Every source below was read on 1 October 2026. Retailer pages are cited only for their own products’ specifications. Where two pages from the same maker disagree, both figures are shown above rather than one picked silently.

1. Royal Horticultural Society, Collecting, storing and reusing water.
2. RSPB, Waterwise gardening: installing a water butt.
3. Strata Products, Slimline Water Butt inc. tap & lid, 100L, including the water butt range table on the same page.
4. Strata Products, Slimline Water Butt inc. tap & lid, 250L.
5. Strata Products, Aqua Tower Water Butt, 200L.
6. Water Butts Direct, 100L Rainsaver kit with stand and diverter, product specification and staff answers on the page.
7. Water Butts Direct, Harcostar 168L water butt with stand and diverter.
8. Water Butts Direct, Grey Harcostar 227L water butt with stand and diverter, product specification and staff answers on the page.
9. Harcostar, 350 Litre Magnum specification sheet (PDF hosted by Water Butts Direct).
10. Water Butts Direct, 350L Magnum Rain Barrel Water Butt (listing gives height 108cm, diameter 78cm).
11. Sotralentz, IBC SLX 1000L technical data sheet (PDF via Traconed).
12. Water Butts Direct, Water butts by capacity.
13. Met Office National Climate Information Centre, HadUK-Grid areal rainfall series: UK, England, Wales, Scotland, Northern Ireland, East Anglia, southern England, Midlands and west Scotland (UK file last updated 1 September 2026). The 1991–2020 averages are GardenCalc’s calculation from these files; the UK 1991–2020 yearly total of 1,162.67mm shown for the UK on the Met Office long-term averages page matches ours.
14. Environment Agency, Rainwater harvesting: regulatory position statement (applies to England, valid until April 2029).
15. U.S. Geological Survey, Water Science School, Water Density: “The density of water is roughly 1 gram per milliliter”.