Table of Contents
- How to Calculate Storage Unit Size Needs: The Short Answer
- The Six-Step Method to Work Out How Much Space You Need
- Quick-Reference Table: Storage Unit Sizes by Home Size
- Using a Storage Size Calculator Without Guessing
- Storage Unit Sizes for a Two-Bedroom House
- Storage Unit Sizes for a Three-Bedroom House
- How to Pack a Storage Unit Efficiently
- Frequently Asked Questions
Last Updated: October 20, 2026
How to Calculate Storage Unit Size Needs: The Short Answer
Add up the cubic metres of everything you plan to store. Divide that total by the usable stacking height. Add 15-20% for aisle space and awkward shapes. Then round up to the nearest unit size.
That is how to calculate storage unit size needs in one breath. At Urban Self Storage, we walk customers through this maths every week at our East Bunbury and Picton facilities, and the same mistake keeps surfacing: people guess from a “fits a two-bedroom house” label instead of measuring. A storage unit size is a floor area in square metres, but your belongings take up volume in cubic metres. Skip that conversion and you either pay for space you never fill or run out of room on moving day.
Below, we show you exactly how to run the six-step method, work through a real two-bedroom example, and use a quick-reference table so you never guess again.
Floor area tells you what you are renting. Volume tells you what you own. The whole calculation is converting one into the other using usable height.
Why Most People Get This Wrong
Most storage guides hand you a “fits X” list and stop there. That is where the errors start.
A 3m x 3m unit sounds generous until you realise the ceiling limits how high you can stack. And a typical 2.4m ceiling does not give you 2.4m of usable height, because you need clearance and safe stacking. Operators vary, so always confirm the actual internal height before you commit.
Three traps catch almost everyone:
- Ignoring usable height. A unit’s advertised size is floor area. Your usable volume is smaller.
- Forgetting aisle space. You need room to walk in, open boxes, and reach the back.
- Mixed box sizes. Odd-shaped boxes leave gaps that waste space.
Get these three right and your estimate lands close to reality.
The Six-Step Method to Work Out How Much Space You Need
Here is the full method, step by step. Work through it once with a pen and paper and you will have a reliable number.
- List every item. Walk each room and write it down. Include the small stuff: boxes, bikes, garden gear.
- Measure length x width x height in metres. Do this for furniture and large items. For boxes, measure one of each size and count how many you have.
- Add the volumes in cubic metres. Multiply each item’s three measurements, then total them.
- Divide by usable stacking height. Take about 2m of a typical 2.4m ceiling, but confirm your operator’s actual height.
- Add 15-20% for access aisle and awkward shapes. This is your buffer space.
- Round up to the nearest unit size. Never round down. Sizing up is cheaper than a second unit.
That final step matters. A size up beats a size down every time when you are close to the line.
Photograph each wall of a room as you list items. It is far easier to spot the things you forgot, like the ironing board or the box under the bed, when you review the photos later.
Worked Example: A Two-Bedroom Unit
Let’s run the numbers on a typical two-bedroom home. These figures are approximate and will vary with your furniture.
- Lounge and dining furniture: about 7 cubic metres
- Two bedrooms, including beds and mattresses: about 8 cubic metres
- Kitchenware and appliances: about 3 cubic metres
- Boxes, linen, and odds and ends: about 2 cubic metres
That totals roughly 20 cubic metres. Divide by 2m of usable height and you get 10 sqm of floor area. Add 15-20% buffer and you land near 12 sqm, so you would round up to a unit around that size.
For most two-bedroom households, a unit in the 9-12 sqm range fits comfortably. Measure your own items before you book, because a home office or a garage full of tools pushes that number up fast.
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Quick-Reference Table: Storage Unit Sizes by Home Size
| Home size | Approx. contents (cubic metres) | Suggested floor area (sqm) |
|---|---|---|
| Studio or one-bedroom | 8-12 | 5-7 |
| Two-bedroom | 15-20 | 9-12 |
| Three-bedroom | 25-35 | 14-18 |
| Four-bedroom | 35-50 | 20-25 |
Treat these as starting points, not gospel. The table assumes average furniture and reasonable packing efficiency. A home with bulky items, or a business storing stock, needs more room.
For business storage, think in pallets and shelving rather than rooms. Stock that stacks high uses less floor area than the same volume spread across low shelves.
Using a Storage Size Calculator Without Guessing
A storage size calculator is a helpful shortcut, but only if you feed it real numbers. Most online tools ask for your home size and spit out a recommendation. That estimate ignores your actual items.
Use a calculator as a cross-check, not the answer. Run the six-step method first, then compare your result to the calculator’s suggestion. If they differ wildly, recheck your measurements.
The calculator cannot see that your sofa does not come apart, or that your mattress must stand upright. Those details change your floor area. So does whether you store furniture assembled or disassembled.
A few practical rules sharpen any estimate:
- Disassembled furniture takes less volume than assembled pieces, but store the screws in a labelled bag taped to the frame.
- Mattresses should stand upright against a wall, not lie flat, so they take up height rather than floor space.
- Appliances like fridges and washing machines can hold boxes inside them, but only clean, dry items.
- Uniform box sizes stack better than mixed ones, so gaps shrink and packing efficiency rises.
Never store a fridge or freezer running, and never pack it with food or damp items. Trapped moisture and odour will damage the appliance and anything stored nearby.
Storage Unit Sizes for a Two-Bedroom House
For a two-bedroom house, a unit of roughly 9-12 sqm usually covers the contents. That is about the size of a small bedroom.
The exact storage unit sizes for a two-bedroom house depend on what you keep. A couple downsizing from a furnished two-bedroom flat sits at the lower end. A family with kids’ furniture, bikes, and a garage of tools sits at the top.
Measure the big three first: beds, lounges, and wardrobes. These drive your volume more than anything else. Then count boxes by size. If you are storing short term during a renovation, you can pack tighter because you will not need frequent access.
If you are unsure, size up. Our team at Urban Self Storage can talk through your inventory list and match it to one of our multi-size units, so you are not paying for empty floor.
Storage Unit Sizes for a Three-Bedroom House
A three-bedroom house typically needs a unit of about 14-18 sqm, assuming average furniture and a garage’s worth of extras.
Storage unit sizes for a three-bedroom house climb quickly once you add a second lounge, a dining set, and outdoor gear. Garden tools, a mower, and patio furniture all take volume, and they rarely stack neatly.
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The smart move here is to plan your layout before you book. Put the items you need least at the back. Keep a clear aisle down the middle. That aisle is your buffer space in action, and it is why the 15-20% allowance exists.
For larger households, or if you are storing a full house plus a caravan or boat, ask about our large storage units in Bunbury and outdoor options. We also offer dedicated caravan storage if a vehicle is part of the move. Every facility has 24/7 CCTV and flexible short and long-term terms, so you are not locked into a contract you do not need.
How to Pack a Storage Unit Efficiently
Knowing how to pack a storage unit efficiently can save you an entire unit size. The goal is simple: fill the height, protect the gaps, and keep a path to the back.
Start with the heaviest, sturdiest items on the floor. Stack boxes on top, largest at the bottom. Stand mattresses and tall boards upright along a wall. Fill appliances and drawers with small items so no space goes to waste.
Four space-saving tips that make a real difference:
- Use uniform boxes. Same-size boxes stack flush and cut wasted gaps.
- Break down what you can. Disassembled bed frames and tables take a fraction of the volume.
- Leave a centre aisle. You will need to reach the back without unloading everything.
- Keep an inventory list. Number each box and note its contents so you are not opening ten boxes to find the kettle.
Draw a simple floor plan on paper before you load. Mark where the big items go and where the aisle runs. Ten minutes of planning saves an hour of reshuffling.
When the maths is done, booking is quick. Our move-in process takes less than 10 minutes, and customers tell us the units are clean, secure, and easy to access. If you would rather see the space first, you can visit either facility before you commit.
Working out how much space you need comes down to measuring, adding a sensible buffer, and rounding up. Get it right and you avoid paying for a unit you barely fill, or worse, running out of room halfway through the move.
Urban Self Storage makes the final step simple. We offer multi-size units across our East Bunbury and Picton facilities, all with 24/7 CCTV surveillance and flexible short and long-term terms. Our team can check your inventory list against available sizes so you book the right fit the first time. Get started with Urban Self Storage and reserve your unit online in minutes.
Frequently Asked Questions
How many cubic metres are in a 3 x 3 m storage unit?
A 3 x 3 m unit has 9 sqm of floor area. With a usable stacking height of about 2 m, that gives roughly 18 cubic metres of volume. The exact figure depends on the operator’s ceiling height and whether you can safely stack to the full usable height, so confirm dimensions before booking.
Should I measure floor area or volume for storage?
Measure volume first. Add up the cubic metres of every item, then divide by the usable stacking height to get the floor area you need. Measuring floor area alone ignores how high you can stack, which is why two households with the same furniture can need different unit sizes.
How much extra space should I allow in a storage unit?
Add 15-20% to your calculated floor area for access aisles, awkward shapes and buffer space. This lets you walk in, reach items at the back and avoid wedging furniture against the walls. If you need frequent access, lean toward 20% rather than 15%.
Can I fit more in a storage unit by stacking?
Yes, stacking is the main way to fit more in. Use uniform boxes, stack them no higher than shoulder level, and keep heavy items low. Mattresses should stand upright, and appliances can be filled with smaller boxes. Disassembling furniture also frees up significant space compared with storing it assembled.