What this calculator works out
Booking a storage unit comes down to matching a size to a job before the contract starts, not after. Too small and you're paying for a second unit or a rushed re-pack within weeks; too big and you're paying every month for floor space nothing ever fills. This tool starts from either a plain description of what's going in, a 1-bed home boxed up, a 3-bed home with furniture, a garage and garden clearout on top, or a volume or floor area you already know, and turns that into a recommended size on the UK square-foot chart or the US named-size chart, set against every other size for comparison.
Two things sit behind every recommendation here rather than being folded quietly into the headline number: the stacking height this tool assumes when it turns a volume into a floor footprint, and the reminder that a size which looks generous on paper can still be worth checking against the size below, once you know how tightly you're willing to pack.
How the recommendation works
Every path here, a home size, a volume, or a floor area, reduces to one figure first: the floor space needed in square feet. A description of what's going in starts from a typical volume for that home size, in cubic feet, adjusted by what's included; a straight volume entry converts directly; a floor area entry skips straight to square feet. Turning a volume into a footprint needs a stacking-height assumption, and this tool uses roughly 2.4 m (8 ft), the height storage providers commonly build their own square-footage figures around and the top of the stacking range Safestore states directly on its own size guide.
Real units are rarely filled as a perfect cuboid, so this is a working estimate rather than a guarantee, the same honest caveat that applies to every rule-of-thumb figure on this page.
Describing a home versus knowing the numbers
The home-size path uses typical volumes cross-checked against how UK and US providers themselves describe each size: a studio flat's contents come to roughly 180 cubic feet, a 1-bed home around 380, a 2-bed around 580, a 3-bed around 780, and a 4-bed or larger around 1,300. Choosing "boxes only" halves that figure, since furniture is what actually eats floor space; "plus garage and garden" adds roughly a third on top, for tools, a mower, bikes and outdoor furniture. If you've already measured a room, added up a few rooms, or know the volume from a moving quote, the volume or floor area path skips the home-size guesswork entirely and works from your own number instead.
A worked example
Take the page's own default: a 1-bed home with furniture. This tool's typical figure for that is about 380 cubic feet (10.8 cubic metres). Divided by the 8 ft stacking assumption, that's about 47.5 square feet of floor space needed. Checked against the UK chart, a 25 sq ft unit is too small and a 50 sq ft unit, a transit-van-sized room, covers it comfortably. That's the same size Safestore's own guide lists as roughly right for a larger 1-bed flat. Switched to the US chart, the same 47.5 sq ft still fits the 5×10 (50 sq ft) unit, the size Public Storage markets directly as suited to a studio apartment's contents, since the US chart runs the same 50 sq ft rung as the UK one at this point.
UK storage unit sizes
The UK chart runs 10, 25, 50, 75, 100, 150 and 200 square feet, the sizes both Big Yellow and Safestore stock as standard rungs, cross-checked between their two published size guides. A 10 sq ft unit is about the size of a telephone box or a large car boot, enough for a few boxes and suitcases; 25 sq ft is a small garden shed, roughly a studio flat's contents boxed up; 50 sq ft is about a transit van or half a single garage; 75 sq ft, a Luton van or a single garage, usually covers a 2-bed home's furniture; 100 sq ft is a full single garage, covering a 2 to 3-bed home; 150 sq ft, one and a half garages, suits a large 3-bed; and 200 sq ft, a standard double garage, covers a 4-bed home or more. Anything bigger moves into bespoke warehouse space quoted directly by the provider.
US storage unit sizes
The US chart runs the five sizes most residential facilities stock as standard, cross-checked between Public Storage's and U-Haul's published size guides: 5×5 (25 sq ft), 5×10 (50 sq ft), 10×10 (100 sq ft), 10×15 (150 sq ft) and 10×20 (200 sq ft). Public Storage's own stated cubic footage for every one of these sizes divides out to an 8 ft ceiling, the same stacking height this tool assumes throughout. A 5×5 suits closet-sized contents; a 5×10 a studio apartment; a 10×10, the most popular size in the US market, around three rooms' worth of belongings; a 10×15 a two-bedroom home; and a 10×20, roughly a one-car garage's footprint doubled, a three-bedroom home including a small vehicle.
Because the US chart has fewer, wider-spaced rungs than the UK chart, the same job can land on a noticeably bigger named size in the US than the square footage recommended in the UK, this tool follows each market's own published sizes rather than smoothing that difference away.
What can't go into a storage unit
A few categories are refused by almost every provider on both sides of the Atlantic, because of the fire, damp or legal risk they carry rather than the space they take up.
- Flammable and hazardous materials. Petrol, gas canisters, paint thinners, fireworks and similar items are a fire risk in an enclosed space and are refused outright.
- Perishable food. Attracts pests and mould in a sealed unit, so fresh or perishable food is not allowed, tinned and dry goods are usually fine.
- Live plants and animals. Units aren't ventilated, heated or cooled to keep anything living safe.
- Illegal or stolen items, and firearms without a licence. Providers can and do inspect on suspicion, and most insist on a signed agreement that nothing illegal is stored.
- Wet or damp items. A wet mattress or a damp box of clothes grows mould that spreads to everything stacked near it, so dry everything fully before it goes in.
Questions people ask
What's the real difference between a 25 sq ft and a 50 sq ft unit?
Roughly double the floor space, but in practice more than double the useful capacity, since a bigger footprint also gives you room to stack without everything toppling. A 25 sq ft unit suits a studio flat boxed up; a 50 sq ft unit comfortably takes a larger 1-bed home's furniture, or a 2-bed home packed in tightly.
Can I get to things stored at the back or under a stack?
Only if you plan for it. A unit packed wall to wall with no gap needs a full unpack to reach anything at the back. If you'll need mid-stay access, leave a narrow aisle down one side and keep anything you might need again near the front and low down, even if that means sizing up slightly.
Do I need insurance for a storage unit?
Most providers require it, either their own policy or proof of separate cover, before they'll hand over keys. Check whether an existing home contents policy already extends to items in storage before paying for a provider's own cover twice over.
What can't I put in a storage unit?
Flammable or hazardous materials, perishable food, live plants and animals, illegal items and firearms without a licence, and anything wet or damp are refused by almost every provider, for fire, pest, mould or legal reasons rather than space.
Is it cheaper to book one bigger unit or two smaller ones?
Usually one bigger unit. Price per square foot tends to fall as units get bigger, and a single unit means a single access visit and a single lock, so two smaller units rarely beat one that covers the same total footprint unless you specifically need to keep two loads apart.
Should I round up from the exact size this tool recommends?
A little, if you can. This tool already builds in a stacking assumption rather than a perfectly packed cube, but real moves collect a few extra boxes between quoting and moving day. If your figure sits close to the top of a size's stated capacity, the next size up buys breathing room for less than it costs to come back and upgrade later.
This calculator uses typical volume estimates per home size and size figures cross-checked between two published guides per market: Big Yellow and Safestore for the UK, Public Storage and U-Haul for the US. Real homes, providers and unit shapes vary; treat the recommendation here as a solid starting point, and confirm exact dimensions, stacking height and access rules with your chosen provider before booking.