Shed Size Calculator
Find Your Perfect Dimensions
Tell us what you need to store and get the exact shed dimensions — floor area, base size, and roof rafter length — in seconds. Works in metric and imperial.
What type of shed are you planning?
Select the option that best matches your project.
Choose your unit system and enter dimensions
Switch between metric and imperial at any time.
What will you store?
Select all items that apply — we'll factor them into your recommended size.
| Measurement | Value | Notes |
|---|
All measurements are estimates. Consult a local builder or structural engineer before ordering materials.
Storage Shed Size Calculator: How Much Space Do You Really Need?
The most common mistake when planning a shed is underestimating storage needs. A practical storage shed size calculator works by summing the footprint of every item you plan to store, adding clearance space for doors and walkways, then rounding up to a standard frame size. As a starting rule, plan for at least 20% more floor area than you think you need — sheds fill up quickly.
For most households storing a lawnmower, basic garden tools, and seasonal items, a floor area of 6–10 m² (65–108 ft²) is the practical minimum. If bicycles, a workbench, or bulk items are involved, target 12–20 m². For a dedicated workshop shed, 20–30 m² gives comfortable working room around equipment. Use our shed size calculator above to get a tailored recommendation rather than guessing from generic charts.
Width matters as much as total area. A narrow, deep shed (e.g. 2 m wide × 6 m deep) is harder to use than a square or wider layout because large items cannot be turned around inside. Aim for a width-to-depth ratio between 1:1.2 and 1:2 for the most usable interior.
Calculating Shed Floor Size: The Formula Explained
Our calculator uses the following approach for calculating shed floor size: it sums the floor footprint of all selected items, applies a 1.25× circulation multiplier for walkways and door swing, then rounds up to the nearest practical frame module (typically 300 mm or 1 ft increments).
Core formula:
Required Floor Area = (Sum of item footprints) × 1.25 (circulation) + door clearance zone
Recommended Width = √(Floor Area × 0.75) [for a 1:1.33 aspect ratio]
Recommended Depth = Floor Area ÷ Recommended Width
For example: storing a ride-on mower (3 m²), two bicycles (2.2 m²), a workbench zone (2.4 m²), and shelving (1.5 m²) totals 9.1 m². Multiplied by 1.25 gives 11.4 m². Rounded to the next module, a 3.0 m × 4.0 m shed (12 m²) is the practical recommendation.
For hay storage, the calculation differs: bale footprint × number of bales ÷ stacking height gives the minimum floor area needed. A round bale (1.2 m diameter) has a footprint of approximately 1.13 m². Fifty bales stacked two high need 28–30 m² of floor area, pointing to a shed of roughly 5 m × 6 m. Our hay shed size calculator handles this automatically.
Shed Roof Rafter Size Calculator: Getting the Right Timber Length
A shed roof rafter size calculator determines the length of timber needed to span from the wall plate to the ridge. Rafter length depends on two variables: the shed's internal width and the chosen roof pitch angle. The formula is:
Rafter Run = Half Width + Eave Overhang (e.g. 0.3 m)
Rafter Length = Rafter Run ÷ cos(pitch angle)
Example: 3 m wide shed, 20° pitch, 0.3 m eave
Run = 1.5 + 0.3 = 1.8 m
Rafter Length = 1.8 ÷ cos(20°) = 1.8 ÷ 0.940 ≈ 1.91 m
Steeper pitches produce longer rafters and therefore cost more timber — but they also shed rain and snow more effectively and give more useful loft headroom. A 15–25° pitch is the most common range for garden and storage sheds. If you live in a heavy-snow region, your local building authority may specify a minimum pitch; always check local requirements.
| Shed Width | Pitch 15° | Pitch 20° | Pitch 30° | Pitch 45° |
|---|---|---|---|---|
| 2.4 m (8 ft) | 1.24 m (4.1 ft) | 1.28 m (4.2 ft) | 1.39 m (4.6 ft) | 1.70 m (5.6 ft) |
| 3.0 m (10 ft) | 1.55 m (5.1 ft) | 1.60 m (5.2 ft) | 1.73 m (5.7 ft) | 2.12 m (7.0 ft) |
| 3.6 m (12 ft) | 1.86 m (6.1 ft) | 1.91 m (6.3 ft) | 2.08 m (6.8 ft) | 2.55 m (8.4 ft) |
| 4.8 m (16 ft) | 2.48 m (8.1 ft) | 2.55 m (8.4 ft) | 2.77 m (9.1 ft) | 3.39 m (11.1 ft) |
| 6.0 m (20 ft) | 3.11 m (10.2 ft) | 3.19 m (10.5 ft) | 3.46 m (11.4 ft) | 4.24 m (13.9 ft) |
Rafter lengths include a 0.3 m eave overhang. Add 50–100 mm to each for birdsmouth notch and ridge lap. Always verify with a structural engineer for larger spans.
Standard Shed Sizes — Reference Table
The table below covers the most common shed sizes used globally for storage, garden, workshop, and hay / farm applications. These are guides only — local frame module standards (300 mm metric, 2 ft imperial) may influence available sizes in your market.
| Shed Size | Floor Area | Best For | Fits (typical items) |
|---|---|---|---|
| 1.8 × 1.2 m (6×4 ft) | 2.2 m² / 24 ft² | Micro storage | Bikes, bins, small tools |
| 2.4 × 1.8 m (8×6 ft) | 4.3 m² / 47 ft² | Basic garden | Push mower + tools |
| 2.4 × 3.0 m (8×10 ft) | 7.2 m² / 77 ft² | Garden / storage | Mower, 2 bikes, shelving |
| 3.0 × 4.0 m (10×13 ft) | 12 m² / 129 ft² | Storage / hobby | Ride-on mower, workbench |
| 3.6 × 6.0 m (12×20 ft) | 21.6 m² / 233 ft² | Large workshop | Full workshop, ATV, vehicle |
| 6.0 × 9.0 m (20×30 ft) | 54 m² / 581 ft² | Small farm / hay | ~40 round bales (2 high) |
| 9.0 × 15.0 m (30×50 ft) | 135 m² / 1453 ft² | Large hay shed | ~120 round bales (2 high) |
| 12.0 × 24.0 m (40×80 ft) | 288 m² / 3100 ft² | Commercial / bulk hay | 250+ round bales or machinery |
Key Factors That Affect Shed Size
Beyond the basic item list, several variables change the right shed dimensions significantly. Our raw material cost calculator can help you estimate material quantities once you have confirmed your dimensions.
Frequently Asked Questions
Start by listing everything you plan to store — lawn equipment, bicycles, tools, or hay bales — then estimate how much floor space each item needs. Add 20–30% extra space for walkways and future items. Our shed size calculator automates this by taking your item list and quantities, then recommending a suitable width, depth, and height.
The shed base should match or slightly exceed your shed's floor footprint. For a standard shed, the base (foundation) is the same width and depth as the floor — for example, a 3 m × 4 m shed needs a 3 m × 4 m concrete or paved base. Our shed base size calculator outputs both the floor area and the recommended base dimensions automatically.
Rafter length depends on the shed width and the roof pitch angle. The formula is: Rafter Length = (Half Width + eave overhang) ÷ cos(pitch angle). For a common 20° pitch on a 3 m wide shed with 0.3 m eave, each rafter runs approximately 1.91 m. Our calculator outputs the recommended rafter length based on your chosen width and pitch, so you can order the right timber lengths.
A hay shed size calculator factors in bale dimensions, stacking height, and the number of bales you need to store. A single round bale (1.2 m diameter) needs roughly 1.5–2 m² of floor space when stacked. For 50 round bales stacked two high, you would need approximately 40–50 m² of floor area. Use the Hay / Farm Shed option in our calculator to get a tailored recommendation.
For a typical garden shed holding basic tools, a wheelbarrow, and a lawnmower, a floor area of 6–9 m² (roughly 2.4 m × 3 m or 8 ft × 10 ft) is a practical minimum. If you also want a small workbench, aim for 9–12 m². Our calculator covers garden and general storage sheds and gives you recommended dimensions based on what you plan to store.