Guide
What size shed do I need?
Shed square footage is the width times the depth: an 8x12 shed is 96 square feet, a 10x12 is 120, a 12x16 is 192. Inside the walls you get less, about 85 sq ft, 108 sq ft and 176 sq ft, because the walls take 3-1/2" on every side.
To choose a size, measure the things that will live in it, lay them out on paper with an aisle to reach each one, and make sure the door is wider than the widest thing you will roll through it. Then pick the smallest shed that fits with room to spare: a shed is cheaper per square foot as it grows, but a permit can depend on its size.
- 8x12
- 96 sq ft (85 sq ft inside)
- 10x12
- 120 sq ft (108 sq ft inside)
- 8x16
- 128 sq ft (114 sq ft inside)
- 12x16
- 192 sq ft (176 sq ft inside)
- Permit sizes to know
- 120 and 200 sq ft (see below)
Shed square footage chart
Every size we have plans for, with its square footage, the floor between the walls and the length of wall you can line with shelves once the door opening is taken out. A 10x16 is 160 square feet outside and 145 sq ft inside; an 8x16 is 128 and 114 sq ft.
| Shed | Square footage | Inside floor | Shelf wall | Door | Materials |
|---|---|---|---|---|---|
| 8x8 gable | 64 sq ft | 55 sq ft | 25 ft | 62" double | $3,141-$3,381 |
| 8x10 gable | 80 sq ft | 70 sq ft | 29 ft | 62" double | $3,415-$3,769 |
| 8x12 gable | 96 sq ft | 85 sq ft | 33 ft | 62" double | $3,670-$4,102 |
| 10x10 gable | 100 sq ft | 89 sq ft | 33 ft | 62" double | $3,853-$4,305 |
| 10x12 gable | 120 sq ft | 108 sq ft | 37 ft | 62" double | $4,095-$4,575 |
| 10x14 gable | 140 sq ft | 126 sq ft | 41 ft | 62" double | $4,540-$4,980 |
| 10x16 gable | 160 sq ft | 145 sq ft | 45 ft | 62" double | $4,905-$5,395 |
| 12x12 gable | 144 sq ft | 130 sq ft | 41 ft | 62" double | $4,436-$4,895 |
| 8x16 gable | 128 sq ft | 114 sq ft | 41 ft | 62" double | $4,257-$4,805 |
| 12x14 gable | 168 sq ft | 153 sq ft | 45 ft | 62" double | $4,861-$5,348 |
| 12x16 gable | 192 sq ft | 176 sq ft | 49 ft | 62" double | $5,201-$5,808 |
| 12x18 gable | 216 sq ft | 199 sq ft | 53 ft | 62" double | $5,561-$6,217 |
| 10x20 gable | 200 sq ft | 183 sq ft | 53 ft | 62" double | $5,519-$6,203 |
| 12x20 gable | 240 sq ft | 222 sq ft | 57 ft | 62" double | $5,904-$6,570 |
| 14x16 gable | 224 sq ft | 207 sq ft | 53 ft | 62" double | $5,644-$6,329 |
| 16x16 gable | 256 sq ft | 238 sq ft | 57 ft | 62" double | $6,139-$6,841 |
| 16x20 gable | 320 sq ft | 299 sq ft | 65 ft | 62" double | $7,025-$7,730 |
| 4x8 lean-to | 32 sq ft | 25 sq ft | 18 ft | 44" single | $2,311-$2,516 |
| 6x8 lean-to | 48 sq ft | 40 sq ft | 22 ft | 44" single | $2,713-$2,994 |
| 8x8 lean-to | 64 sq ft | 55 sq ft | 26 ft | 44" single | $2,894-$3,203 |
| 8x10 lean-to | 80 sq ft | 70 sq ft | 29 ft | 62" double | $3,401-$3,775 |
| 8x12 lean-to | 96 sq ft | 85 sq ft | 33 ft | 62" double | $3,551-$3,995 |
| 10x10 lean-to | 100 sq ft | 89 sq ft | 33 ft | 62" double | $3,705-$4,042 |
| 10x12 lean-to | 120 sq ft | 108 sq ft | 37 ft | 62" double | $3,895-$4,269 |
| 10x14 lean-to | 140 sq ft | 126 sq ft | 41 ft | 62" double | $4,243-$4,614 |
| 12x12 lean-to | 144 sq ft | 130 sq ft | 41 ft | 62" double | $4,299-$4,652 |
The calculator and plans cover any size from 4 to 20 feet in half-foot steps, not only these.
How to work out the size you need
- List what goes in. Mower, wheelbarrow, bikes, bins, tools, the things that will come later. Write down each one's footprint (length and width) at its widest.
- Draw the floor. On squared paper, one square to a foot, draw the inside floor of a size from the chart and place each item. Leave an aisle you can walk down with your arms full to reach every item without moving another.
- Use the walls. Shelves, hooks and pegboard hold the small things, so the floor is for what has to stand on it. The chart's shelf-wall column is how much inside wall each size gives you.
- Check the door and the height. The door must clear the widest item; long tools need the height (our walls are framed 8' 1-1/8" tall).
- Add room to grow. If two sizes both fit, the bigger one usually costs less per square foot. Before you decide, check the permit size limits where you live.
Pick the door before the size
For anything with wheels the door decides more than the floor. Our plans offer four door openings, measured as the framed rough opening: 38" single, 44" single, 62" double, 74" double. The width you can drive through is a little less once the doors and trim are hung.
Most of our plans default to the 62-inch double door. The smallest lean-tos (4x8, 6x8, 8x8) take a 44-inch single, because their tall front wall needs solid wall beside the opening to stay braced. Measure a riding mower or a tractor at its widest point, with its deck and chute as they will be when you drive in, and compare it with the opening, not the shed's size.
Size and permits: 120 and 200 square feet
Two numbers come up when towns decide whether a shed needs a building permit. The International Residential Code, a model code many towns adopt for homes and their sheds, exempts one-story detached accessory buildings up to 200 square feet, and the International Building Code exempts tool and storage sheds up to 120 square feet. Your town may use either number, or its own, and zoning rules still apply.
- At or under 120 sq ft: 4x8, 6x8, 8x8, 8x10, 8x12, 10x10, 10x12.
- Over 120, at or under 200 sq ft: 8x16, 10x14, 12x12, 10x16, 12x14, 12x16, 10x20.
- Over 200 sq ft: 12x18, 14x16, 12x20, 16x16, 16x20.
Read do I need a permit for a shed? for what to ask your town before you choose.
A bigger shed costs less per square foot
Doors, windows, hardware and the roof edge cost much the same whatever the size, so each extra square foot is cheaper than the last. In materials, an 8x8 gable comes to $49.08 a square foot and a 16x20 to $21.95.
| Shed | Materials | Per sq ft of floor |
|---|---|---|
| 8x8 gable | $3,141 | $49.08 |
| 8x12 gable | $3,670 | $38.23 |
| 10x12 gable | $4,095 | $34.12 |
| 12x16 gable | $5,201 | $27.09 |
| 12x20 gable | $5,904 | $24.60 |
| 16x20 gable | $7,025 | $21.95 |
Every size's full price table, by siding and roofing, is on the shed cost pages, for example what a 10x12 costs to build.
Sizes in between, and the roof
If the one you need is not in the chart, say a 9x11 or a 14x18, the free materials calculator lists the materials for it. A gable roof gives more headroom and a small loft space; a lean-to has one slope that can sit against a fence line or the back of a garage. See gable vs lean-to on the same footprint.
Questions people ask
How many square feet is a 10x12 shed?
A 10x12 shed is 120 square feet, measured to the outside of the framing. The floor between the walls is about 108 sq ft.
What is the square footage of an 8x12 shed?
96 square feet (8 times 12), or about 85 sq ft inside the walls.
How big is an 8x16 shed?
An 8x16 shed is 128 square feet, about 114 sq ft inside, with 41 feet of inside wall for shelves.
What size shed do I need for a riding mower?
Start from the door: measure the mower at its widest, deck and chute included, and choose a door opening wider than that. Our plans offer openings up to 74 inches (a double door). Then draw the floor to check there is an aisle beside the mower for your tools.
What size shed can I build without a permit?
It depends on your town. The model codes that towns start from exempt sheds up to 200 square feet (International Residential Code) or 120 square feet (International Building Code), and many towns change those numbers. Ask your building department and zoning office before you build.
Try a size
Put any size into the free materials calculator for its full list of materials and price, or open the 10x12 gable shed plans to see what the plans hold.
Sources
- Washington State IRC 2018, Section R105.2 (via the City of Lynnwood): the 200 square foot exemption for one-story detached accessory structures
- International Code Council, 2021 IBC Section 105.2 (in a committee proposal): the 120 square foot exemption for tool and storage sheds
Our plans and these guides follow common light-frame building practice and are a guide, not drawings stamped for your site: check your local codes, permit rules and HOA before you build.