What this calculator works out
This calculator estimates the practical storage volume of a run of shelving from its width, height and depth, applying a usable percentage, and reports the total shelf surface across the levels you specify.
The usable percentage is what makes the figure realistic. Boxes do not tessellate, access needs space, and nobody fills shelving to the ceiling of every bay.
Enter your details
Before you plan
- Measure the space the shelving will occupy, not the garage. Leave room to open a car door if the garage still holds a car.
- 75% usable is a reasonable default. Uniform stackable boxes push it higher; awkward items push it much lower.
- Check the shelf load rating. Cheap shelving is often rated per shelf, and the rating assumes an evenly distributed load.
- Garages are damp. Anything stored in one needs protecting from moisture regardless of the shelving.
The cubic metre figure tells you how much stuff fits. The square metre figure tells you how much you can lay out and see. For a garage the second often matters more — storage you cannot reach or find is not much better than not having it.
How this calculator works
A bay volume and a shelf surface:
Practical volume = width × depth × height × (usable % ÷ 100)
Total shelf surface = width × depth × number of levelsThe volume figure describes the whole bay envelope, so it does not change with the number of shelf levels — more levels divide the same space differently rather than creating more of it. The surface figure is the one that responds to adding shelves.
Worked example: a 3 m run of shelving
Using the default figures — 3 m wide, 2 m high, 0.5 m deep, 5 levels, 75% usable:
- Practical storage: 2.25 m³
- Total shelf surface: 7.5 m²
2.25 m³ is roughly 45 standard 50 litre storage boxes, which is more than most garages actually need shelving for. The 7.5 m² of surface is the more useful figure for tools, paint and things you want visible. Note that 5 levels over 2 m gives 40 cm of clear height per shelf before the shelf thickness — fine for boxes, too low for a stepladder or a bicycle.
Common mistakes
- Using 100% usable. Real packing efficiency is well below that.
- Ignoring shelf load ratings. They are usually per shelf and assume even distribution.
- Spacing shelves evenly regardless of contents. Mixed shelf heights are far more useful.
- Storing directly on a garage floor. Concrete draws moisture; keep things raised.
- Filling the space the car needs. Measure with the door open.
Frequently asked questions
How much weight can garage shelving take?
It varies enormously. Budget plastic shelving may be rated at 20 to 30 kg per shelf, steel boltless units at 150 to 300 kg, and heavy-duty racking considerably more. The rating assumes an evenly distributed load — a concentrated point load in the middle of a shelf is a different matter. Fixing tall units to the wall is worth doing regardless of rating.
What should not be stored in a garage?
Anything that suffers from damp or temperature swings: paint, which separates and freezes; documents and photographs; upholstered furniture; electronics; and most food. Petrol and gas cylinders have specific storage requirements and quantity limits. Damp is the main enemy, and an unheated garage is often damper than an outbuilding.
How do I keep a garage dry?
Ventilation first — most garages are damp because moist air cannot escape. Keep airbricks clear, check for a failed damp-proof course, avoid storing anything against outside walls, and raise items off the floor on pallets or shelving. A dehumidifier helps in a sealed garage but treats the symptom.
Is it worth converting the garage instead?
It depends what the space is worth to you. Garage conversion is generally permitted development if it stays within the existing structure, but building regulations apply for insulation, damp proofing, ventilation and structure. It is a substantial project, and losing off-street parking can affect resale in some areas.
Is what I enter stored?
No. Dimensions are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — permitted development and building regulations for garages and conversions
- Health and Safety Executive — safe storage, racking stability and manual handling
Sources are checked at publication and can change — how I choose and check references.