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ShedCalc
Free & unbiased — we don't sell sheds

Shed Size Calculator

Stop guessing at square footage. Tell us what you'll actually store and we'll recommend the right footprint — with the access space, growth room, and permit thresholds factored in.

  • Sized from your inventory
  • Every assumption shown

What will you store?

Add the things going in. We'll work out the footprint you need.

  • Push mower

    6 sq ft

    0

  • Self-propelled mower

    9 sq ft

    0

  • Riding mower / tractor

    24 sq ft

    0

  • Wheelbarrow

    8 sq ft

    0

  • Garden tool rack

    3 sq ft · can be hung

    0

  • Hose reel

    4 sq ft · can be hung

    0

  • Fertilizer spreader

    6 sq ft

    0

  • Snow blower

    10 sq ft

    0

Walk around everything: Reach any item without moving another.

Add at least one item to get a recommendation.

Your recommended size appears here

Add what you'll store, choose how you'll use the space, then press Calculate my shed size.

Getting the size right

How to work out what size shed you need

The honest method — start from your stuff, not from a catalogue.

Why most shed size calculators are useless

Search for a shed size calculator and you'll mostly find tools that multiply length by width. That's not a calculator — it's arithmetic, and it answers a question you didn't ask. The real question is "what size do I need?", and the only way to answer it is to work backwards from what you're actually putting inside.

That's what this tool does. You list your items, tell it how you'll use the space, and it returns a recommended footprint — showing exactly how it got there. Because we don't sell sheds or take retailer commissions, nothing is nudging the answer upward.

How to use it, step by step

  1. 1. Add what you'll store. Work through the categories and set quantities. Include the things you'll add later, not just what you own today.
  2. 2. Choose how you'll use it. Storage-only needs far less floor than a space you'll work in — this single choice moves the answer more than anything else.
  3. 3. Flag wall storage. If you'll hang bikes, ladders and tools, switch it on and we credit back half their footprint.
  4. 4. Calculate, then compare. You get a recommended size plus a tighter and roomier option, each linking to a full material list.

Understanding your result

The result is built in three layers. First, the item area — the raw floor your belongings occupy. Then an access allowance, because you need aisles, door swing and room to reach things: ×1.4 for pure storage, ×1.7 to move around comfortably, ×2.1 if you'll work inside. Finally a 15% growth allowance, because the single most common shed regret is buying too small.

We then round up to the nearest standard shed size — the ones real builds actually use — and show the floor-utilisation percentage so you can see how full the shed will feel.

Size and permits: two thresholds that matter

Size doesn't just affect what fits — it affects whether you need approval. Two numbers come up repeatedly: 120 sq ft, an older limit many local codes still enforce, and 200 sq ft, the exemption for one-storey accessory buildings in the current International Residential Code (IRC R105.2).

Because jurisdictions adopt codes at different times and add their own amendments, your local rule could be either — or something else entirely. Height, foundation type and distance from property lines usually matter too. The calculator flags which side of both thresholds your recommended size falls on, but the only authoritative answer comes from your local building department. See our disclaimer — this is general guidance, not code advice.

Common sizing mistakes

  • Measuring only the items. A shed packed wall-to-wall is a shed you can't use.
  • Forgetting the door swing and the path to get a mower in and out.
  • Sizing for today. Storage needs grow; plan for it now, not with a second shed later.
  • Ignoring vertical space. Walls and overhead are free floor space you haven't used yet.

Once you know the size

With a footprint chosen, the next question is what it costs to build. Every size links straight to a full shed size guide with a pre-calculated material list, and the free Shed Material Calculator turns your exact dimensions into an itemised, shopping-ready list — studs, siding, sheathing and roofing — with the math shown and a 10% waste factor included.

Questions

Shed size FAQ

Straight answers on sizing, access space, and permit limits.

What size shed do I need?
It depends on what you'll store and how you'll use the space, not on a round number. Start by listing your largest items — mower, bikes, workbench, bins — then add room to walk around them and open the door, plus a little space to grow into. This calculator does exactly that: it turns your inventory into a recommended footprint and shows the math behind it.
How much extra space should a shed have beyond the items?
More than most people expect. You can't fill a shed to 100% and still use it. This calculator adds an access allowance based on how you'll use the space — ×1.4 for grab-from-the-door storage, ×1.7 to reach everything comfortably, and ×2.1 if you'll actually work inside — then a 15% growth allowance on top, because sheds fill up faster than anyone plans for.
What size shed can I build without a permit?
It varies by location, and two thresholds matter. Many local codes still use a 120 sq ft limit, while the current International Residential Code (IRC R105.2) exempts one-storey accessory buildings up to 200 sq ft. Your local rules override both, and height, foundation and distance from property lines also count — so always confirm with your local building department before you build.
Is a 10x12 shed big enough?
For many households, yes. At 120 sq ft a 10×12 comfortably holds a riding mower plus tools, a wheelbarrow, shelving and seasonal storage with room to walk around — which is why it's the most popular size. If you're adding a workbench and want clear floor to work on, step up toward 10×16 or 12×16. Run your actual inventory through the calculator to see where you land.
Does wall storage change what size shed I need?
Yes, meaningfully. Hanging bikes, ladders, hoses and long-handled tools on walls or overhead frees up the floor they'd otherwise occupy. Switch on the wall-storage option and the calculator credits back half the footprint of items that can realistically be hung — which is often enough to drop you a size.
Should I size up or size down if I'm between two shed sizes?
Size up, almost always. The most common shed regret is buying too small, and the cost difference between adjacent sizes is usually modest compared with the cost of replacing a shed you've outgrown. The main reasons to size down are yard space, budget, and permit thresholds — a slightly smaller shed can keep you under a limit that would otherwise trigger an approval.
Are the item sizes in the calculator accurate?
They're typical real-world footprints for each item, and they vary by model — a compact push mower and a large self-propelled one aren't identical. Treat the result as a well-reasoned starting point, and if you own something unusually large, measure it and size up accordingly. Every assumption is shown so you can sanity-check the result.
Is this shed size calculator free?
Completely. No sign-up, no email, no sales pitch. We don't sell sheds or take retailer commissions, so nothing here is tuned to push you toward a bigger building than you need — which is exactly the problem with most size tools.

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