What size storage unit do you actually need?

Every self-storage website has the same chart: a five by five holds a studio, a ten by ten holds a two-bedroom house, and so on. It is a rough guide written by people whose interest is that you book something, and it is wrong in both directions surprisingly often.

Here is a better way to arrive at the number.

Count in boxes and large objects, not bedrooms

Two households with the same number of bedrooms can differ by a factor of three. What actually determines the space is:

• How many standard boxes you will have
• How many large items that cannot be stacked on — sofas, mattresses, wardrobes, appliances
• How many awkward items — bicycles, exercise equipment, ladders, garden furniture

A standard medium box is roughly a foot and a half cubed. Fifty of them stack into about a hundred cubic feet of actual box, which is nothing like a hundred cubic feet of unit.

The three things that make a unit smaller than it looks

You have to leave a walkway. Unless you are prepared to unload the whole unit to reach the back, budget about fifteen percent of the floor for a corridor. It is the single best trade you can make in a unit, and it costs floor space.

You cannot safely stack to the ceiling. Most units are eight feet or more, and boxes above head height are a genuine hazard to retrieve. Plan on stacking to about six feet unless you keep steps in there.

Furniture does not tessellate. A sofa is not a cuboid. Awkward shapes waste the space around them, and a unit full of furniture holds far less than its volume suggests.

Between them, these mean the usable capacity of a unit is roughly sixty to seventy percent of the advertised volume.

Rough starting points

Adjusting for the above, in practice:

• 5x5 (25 sq ft): a large cupboard. Seasonal things, boxes, a bicycle. Not furniture.
• 5x10 (50 sq ft): the contents of a single room, or a studio flat without the large furniture.
• 10x10 (100 sq ft): the usual answer for a small two-bedroom home, including sofas and a bed, if packed deliberately.
• 10x15 (150 sq ft): a three-bedroom house, or a two-bedroom with a lot of equipment.
• 10x20 (200 sq ft): a family house, or a house plus a car's worth of other things.

Go up a size if any of these are true

• You will be adding to it over time rather than filling it once
• You need to get at things regularly, rather than sealing it for a year
• You are storing anything long and rigid — ladders, timber, surfboards, skis
• You have not packed yet and are estimating from an unpacked house, which almost always underestimates

That last one is worth dwelling on. An unpacked house looks smaller than it is because much of the volume is inside cupboards.

Go down a size if all of these are true

• You have already packed and can count the boxes
• Everything is in uniform stackable containers
• Nothing needs retrieving until you empty the whole thing
• You have measured the large items rather than guessed

Measure the door, not just the floor

The most expensive mistake in unit selection is not floor area. It is a unit whose door is too narrow for a sofa or too low for a wardrobe standing up.

Check the door opening dimensions and the corridor width to the unit, particularly in indoor multi-storey facilities where the lift may be the real constraint.

What to do before you book

• Pack, or at least box, everything you can
• Count the boxes and measure the large items
• Add fifteen percent for a walkway and cap stacking at six feet
• Then pick the size

If you are between sizes, the smaller one plus a genuinely disciplined layout usually beats the larger one filled carelessly — but only if you actually keep the discipline.

Once you have it, know what is in it

Whatever size you end up with, the thing that determines whether it stays useful is whether you can find things without emptying it. Numbered bins and a record of the contents is the whole trick. Waoo Storage prints a QR label for each bin so you can scan it and see inside, and it works with no signal, which most units have none of.