What Size Shed Do I Need? A Practical Sizing Guide
Almost nobody wishes they had built smaller. After more than 12,000 buildings, the regret we hear most often is about the size someone talked themselves out of. This guide walks through how to work out the footprint you actually need, and where the thresholds sit that are worth knowing before you decide.
Start With What Goes In, Then Add the Space Around It
The usual mistake is measuring the objects and stopping there. For example, a standard mower is about 2 by 5 feet, so a 6×8 space sounds generous. In practice, you may also need to store oil, gas, and other lawn care tools and materials.
A reliable rule: measure the footprint of everything going in, then double it. That second half is circulation, and it is the difference between a building you use comfortably and a building you dread opening.
Sizes We Build and What They Hold
Small: 32 to 80 square feet
4×8, 6×8, 8×8, 8×10
Yard tools, a mower, bikes, garden supplies. The 4×8 is genuinely useful for organizing equipment and tools, but it is storage only. Anything you want to stand and work inside should start at 8×8.
Medium: 96 to 144 square feet
8×12, 10×10, 8×14, 10×12, 12×12
This is where most projects land. A 10×10 fits shelves and a workbench, a 10×12 makes a comfortable one-person office, and a 12×12 has room for a second chair or a home gym. Every size here stays under the 200 square foot permit exemption most jurisdictions use.
Large: 160 to 200 square feet
10×16, 12×14, 12×16, 10×20
Workshops, gyms, studios, and buildings split into two rooms. A 12×16 at 192 square feet is the largest common size that still fits under a 200 square foot exemption.
Larger than That, Expect a Building Permit To Be Required
The Original Mini Barns partners with local architects, engineers and other professionals to bring together a trustworthy team to assist with your project. Whether it’s a DADU, a golf simulator, a virtual reality room or another entertainment space, the OMB team is here to help.
Three Thresholds Worth Knowing
- 120 square feet. Together with a total height limit of 12 feet, this is Seattle’s maximum permit exemption.
- 200 square feet. The exemption most local jurisdictions use, including unincorporated Snohomish and King County. 12×16 is the most popular standard size underneath it.
- 12-foot width. Gables and gambrels over 12 feet wide typically require manufactured trusses and come with additional costs, and side walls longer than 12 feet should include a spreader element such as a loft to keep the walls from spreading.
These are general size and threshold guidelines, not permission. Check with your local jurisdiction for what the current exemptions actually cover, because local land use and building codes continuously evolve, and in the end it’s your responsibility to verify and comply.
Height is the Dimension People Forget
Our standard internal wall height is 7 feet 4 1/2 inches, and it can be upgraded or reduced. This can be a factor for storage, but it matters more for a gym, where overhead pressing and pull-up bars need clearance, or a workshop where you are standing sheet goods on end. Roof style affects this too: the Rancher’s 6:12 gable and the Craftsman’s 12:12 both add height at the peak, while the Forester’s single slope gives you one tall wall.
Use the Vertical Space
A storage loft is the best value addition we sell, because it uses volume that is otherwise wasted. This space can be maximized with our Craftsman (12:12 roof pitch) or Barn (gambrel-style) roof options, or by adjusting the wall height and loft placement. As a general guideline, loft spaces should stay within a maximum height of 7 feet for the building to be considered a permit-exempt structure.
Getting it In and Out
A standard single door is 36 or 42 inches wide. That’s sufficient for tools and boxes, but it can make it difficult to move larger items such as a couch, desk, assembled squat rack, treadmill, or seasonal yard furniture into the space. Double doors at 36 or 42 inches wide cost a bit more but are almost impossible to regret. If you have a gravel foundation, add a composite ramp or stairs to make that step up easier to navigate.
Check the Lot Before the Building
Two constraints bind before your wish list does. Setbacks dictate how close you can get to property lines, and lot coverage limits the combined footprint of every structure on the parcel, including the house, garage and raised decks. In most urban residential zones that ceiling is roughly 50 to 60 percent. Work out the buildable rectangle first, then size within it.
Also think about access on installation day. We typically arrive with panelized wall and roof sections, and our crew needs an accessible route to the pad. A path 3 feet wide by 10 feet tall is generally required.
The Honest Recommendation
If you are choosing between two adjacent sizes and the larger one fits your lot, your budget and your permit position, take the larger one. The incremental cost per square foot falls as buildings get bigger, and the cost of replacing a building that turned out too small is the whole thing over again.
The simplest way to test a layout is our free 3D Shed Builder, where you can set the size, style, doors and windows and see the result before speaking to anyone. It also gives you a rough floor plan, so you can see what will fit in the structure.
Sizing Questions
What is the most popular shed size?
10×12 and 12×16 are our most popular sizes. Sizes between 100 and 200 square feet account for most of what we build, and these two are common because they are large enough to be genuinely useful while staying under the 200 square foot permit exemption most local jurisdictions apply to accessory structures.
What size shed fits a riding mower?
8×10 is the minimum for a riding mower, with double doors. A riding mower needs turning space and a wide enough opening, and a single 36 inch door will make every trip awkward. If the shed also holds tools and garden supplies, 10×12 or larger would be a more comfortable choice.
How big should a backyard office be?
Most backyard offices are between 100 and 200 square feet. 10×10 at 100 square feet suits one person with a desk, chair and filing system. Go to 10×12 or 12×12 if you want a couch or a mounted monitor or TV, and 12×14 or larger for a treatment room, a recording space or two people working. Note that offices customers visit are treated differently from a remote working space.
Can you build larger than 12×20?
Yes, we build larger than 12×20. The published price list runs to 12×20 at 240 square feet, but we build beyond it, including a recent 410 square foot workshop and storage building. Larger structures need a permit and often benefit from architect involvement, both of which we can help arrange.
Does a bigger shed cost more per square foot?
No — a bigger shed generally costs less per square foot. A 4×8 Rancher works out around $95 per square foot, while a 12×20 Rancher is closer to $57. Fixed costs such as delivery, the door, the roof structure and the crew’s time are spread across more floor area. It is one reason going a size up is usually good value. At the upper end, manufactured trusses, more substantial foundations and permit requirements are added to the equation.
How much clearance do I need around the building?
Your local setback rules are the binding constraint, so check those first. Beyond that, if the structure is not right next to the house, a 6 foot separation is generally required so emergency personnel can get through the space. Requirements differ between jurisdictions, so check your local rules before deciding where to build. If you’d like assistance with this, contact The Original Mini Barns and we’ll do our best to assist.
Try a Size Before You Commit
Build it in 3D and see how it looks, or tell us what is going inside and we will help you size it.
