What Size Shed Is 120 Square Feet? 10x12 and Other Sizes

Last updated October 20, 2026

What size shed is 120 square feet? Usually a 10×12 or a 12×10, since 10 times 12 is 120. An 8×15 or 6×20 also makes 120 sq ft, but few plans use them. By area, 100 sq ft is a 10×10, 140 to 150 is a 10×14 or 12×12, and about 200 is a 10×20, 12×16 or 14×14.

Plan sizes and door widths below come from our 3DSHEDPLANS plan pages. Door widths are as each plan page lists them; the clear opening after jambs and trim is a few inches narrower, so measure your mower against that.

Shed sizes by square feet: the quick chart

A shed’s size is its outside floor frame, length times width. The inside column assumes 2×4 walls, which take about 3 1/2 inches on every side, so a shed loses about 7 inches in each direction. That is the bare-stud number. Lining the walls with 1/2 inch OSB or drywall takes about another inch each way.

Target area	Common sizes (sq ft)	Floor inside, 2×4 walls	Our plans at this size
About 100 sq ft	10×10 (100), 8×12 (96)	about 89 / about 85 sq ft	10×10 gable, 10×10 lean-to, 8×12 gable
120 sq ft	10×12 or 12×10 (120)	about 108 sq ft	10×12 gable, 12×10 gable, 10×12 lean-to, 10×12 hip roof
140 to 150 sq ft	10×14 (140), 12×12 (144)	about 126 / about 130 sq ft	10×14 gable, 12×12 gable
160 to 170 sq ft	10×16 (160), 8×20 (160), 12×14 (168)	about 145 / 144 / 153 sq ft	10×16 gable, 8×20 gable, 12×14 gable, 12×14 lean-to
About 200 sq ft	12×16 (192), 14×14 (196), 10×20 (200)	about 176 / 180 / 183 sq ft	12×16 gable, 14×14 lean-to, 10×20 gable

To work out the inside floor of any size, take 7 inches off the length and the width, multiply, and divide by 144. A 10×12 becomes 113 by 137 inches, which is 15,481 square inches, or about 108 sq ft.

What size shed is 120 square feet, and is 10×12 or 12×10 better?

A 120 sq ft shed is a 10×12 or a 12×10: the same floor turned 90 degrees. The real difference is which wall gets the door and how wide that door is. Sellers write the two numbers in either order, so check the drawings.

• Our 10×12 gable shed plan is 12 ft wide and 10 ft deep, with a 60 inch double door (rough opening) on the 12 ft front wall, so the back wall is only 10 ft from the door.
• Our 12×10 gable shed plan has a 39 inch single door; check its drawings for the door wall. It suits a garden or tool shed you walk into rather than wheel into.

An 8×15 has the same 120 sq ft, but at about 7 ft 5 in wide inside, shelves on both long walls leave a narrow aisle. A 10×12 is the easier room to use.

A 10×12 also sits exactly on 120, a size line some towns use. “Up to 120” and “under 120” are not the same, and an office that measures to the roof edge will count a 10×12 with 6 inch overhangs as about 11×13, or 143 sq ft. An 11×11 is 121 sq ft, just over. If your line is 120, check your local permit office for how they measure before you buy a plan.

What size shed is 100 square feet?

A 10×10 is the common size that lands on 100 sq ft. Inside, with 2×4 walls, it is about 9 ft 5 in square, or about 89 sq ft of floor.

An 8×12 (96 sq ft) is the usual alternative. It has almost the same area but is 2 ft narrower.

With 16 inch shelves on one long wall, an 8×12 still leaves an aisle of about 6 ft, which is plenty for a push mower. A 10×10 gives a squarer room for a potting bench or a small workshop corner. Our 10×10 shed ideas and layouts article shows a few ways to set one up.

What size shed is 150 square feet?

Exactly 150 sq ft is a 10×15. Few plans or kits use it, because lumber is sold in 2 ft length steps (8, 10, 12, 14 and 16 ft). A 15 ft wall means cutting a foot off 16 ft boards. Most builders round to a stock size:

• 10×14 (140 sq ft). Our 10×14 gable shed plan has a 78 inch double door.
• 12×12 (144 sq ft). Square, with a 78 inch double door on our 12×12 gable shed plan.
• 10×16 (160 sq ft). A long wall for bikes and shelving, with a 78 inch double door on our 10×16 gable shed plan.

The 12×12 is square, so a mower can turn on either side. The 10×16 gives the most wall for shelves and hooks.

What size shed is 200 square feet?

A 10×20 is exactly 200 sq ft. A perfect square of 200 sq ft would be about 14 ft 1 3/4 in on each side, so the practical square is a 14×14 at 196 sq ft. A 12×16 at 192 sq ft is the other near-200 size.

Inside sizes of the three:

• 10×20: long and narrow, about 9 ft 5 in by 19 ft 5 in. Our 10×20 gable shed plan has a 78 inch double door plus a 36 inch side door, so you can reach the back without walking past everything.
• 12×16: about 10 ft 5 in by 15 ft 5 in, or about 176 sq ft. Our 12×16 gable shed plan with a double door has a 78 inch double door.
• 14×14: the squarest, about 13 ft 5 in on each side, and good for a workshop with a bench in the middle. Our 14×14 lean-to shed plan has an 84 inch door.

What fits in each size class

• About 100 sq ft: a push mower, wheelbarrow, rakes and shovels, a bike, and shelves on one or two walls.
• 120 sq ft: the same plus a second bike or a narrow riding mower, if the door clears the mower at its widest point.
• 140 to 170 sq ft: a lawn tractor plus garden gear, with a 78 inch or wider door. Measure the tractor with its deck on and leave a few inches each side.
• About 200 sq ft: a tractor, a snow blower, bikes and full shelving, or a workshop with a bench and room to move around it.

Our what size shed do I need guide has a five-step layout method and mower door widths in more detail.

Why sheds come in 2 ft steps

Lumber comes in 2 ft length steps, such as 8, 10, 12, 14 and 16 ft, so walls in even feet use stock boards with little waste. Plywood, OSB and sheet siding come in 4 ft by 8 ft sheets, so sizes in multiples of 4 ft (8, 12, 16, 20) use whole sheets. A 10 ft or 14 ft wall leaves a half sheet, which usually gets used elsewhere on the shed.

An odd size like 10×15 or 11×13 is possible, but you pay for the offcuts and spend time on extra cuts. If you need a little more floor, one standard size up usually costs less than an odd size in between.

More storage without more square feet

If a size line or your yard caps the floor area, build up instead of out:

• Shelves to the top plate. Our gable plans have walls about 7 ft 10 in tall on most sizes, measured as framing height, so shelves can run well above head height. Fasten tall shelving to the studs.
• A loft over the ceiling joists for light, seldom-used items, but only if the plan or a builder sizes those joists for storage. Rafter ties on many gable sheds are not meant to carry a load. Some offices count a loft in the floor area, so ask. Our shed loft headroom guide shows how much room a loft leaves by size.
• Wall hooks and racks for bikes, ladders and long tools.

A taller shed can run into a height limit instead, so check your local permit office about height as well as area.

How towns count shed square feet

Many local rules use square feet, so a size on paper can land on either side of a line. Check your local permit office before you settle on a size near any limit. Some examples of how the numbers vary:

• The model International Residential Code (2021), Section R105.2 lists one-story detached storage sheds with no more than 200 sq ft of floor area among its permit exemptions. Towns adopt and amend it, and some use lower lines, like the two 120 sq ft examples below.
• Hermiston, Oregon, publishes a shed and accessory structure page with a zoning review for sheds of 120 sq ft or more.
• Lee, Massachusetts, explains when a shed needs a permit, using 200 sq ft for sheds at a one or two family home and 120 sq ft for sheds at other properties.

“Up to 200” and “under 200” are not the same, so a 10×20 can fall on either side. Some offices measure the roof or the outside of the siding rather than the floor frame, and overhangs add to that. Height and distance from the property line can matter as much as area. Our shed permit checklist lists the questions to ask.

The base grows too. Many builders run a gravel pad about 1 ft past the floor frame on every side, so a 10×12 shed sits on a pad about 12×14.

Common mistakes when picking a size by square feet

• Comparing areas, not shapes. An 8×20 and a 10×16 are both 160 sq ft, but the 8×20 is 2 ft narrower inside.
• Planning from the outside size. Shelves 16 to 24 inches deep come off the inside size, not the number on the plan.
• Ignoring the door. A 200 sq ft shed with a 36 inch door still cannot take a lawn tractor.
• Building right at a size line without asking. Measured to the roof edge, a 12×16 with overhangs can be over 200 sq ft. Check your local permit office first.
• Picking an odd size to gain a few feet. You pay for offcuts and extra cuts.

What we checked: the 200 sq ft model exemption from the ICC’s IRC 2021 text, the town lines from Hermiston’s and Lee’s own pages, and plan sizes and door widths from our plan pages. Inside areas are our arithmetic for 2×4 walls.

Plans that fit

Every 3DSHEDPLANS plan is a $19.99 PDF with a full material list, cut list and step-by-step 3D images. Browse every size on the shed plans page, or start with the size class you need:

• 100 sq ft: the 10×10 gable shed plan, 39 inch door.
• 120 sq ft: the 10×12 gable shed plan, 60 inch double door.
• About 150 sq ft: the 12×12 gable shed plan, 78 inch double door.
• About 200 sq ft: the 12×16 gable shed plan with a double door at 192 sq ft, or the 10×20 gable shed plan at 200 sq ft.

Want to see the format first? Download the free 10×12 gable shed plan preview PDF. Our shed cost guide shows how cost grows with size, and the gable shed plans and lean-to shed plans pages list every size by roof style.

Frequently asked questions

What size shed is 100 square feet?

A 10×10. It is the common size that lands right on 100 sq ft. An 8×12 is close at 96 sq ft but is 2 ft narrower, which matters if you want to park a mower and still walk past it.

What size shed is 150 square feet?

Exactly 150 sq ft is a 10×15, which few plans or kits use. Most people pick a 12×12 (144 sq ft), a 10×14 (140 sq ft) or a 10×16 (160 sq ft) instead.

What size shed is 200 square feet?

A 10×20 is exactly 200 sq ft. A 12×16 (192 sq ft) and a 14×14 (196 sq ft) sit just under 200, handy if your local size line is 200. Check your local permit office for how they measure before you build right at a size line.

How much floor space is inside a 10×12 shed?

With 2×4 walls, about 108 sq ft. Each wall is about 3 1/2 inches thick, so the floor inside is roughly 9 ft 5 in by 11 ft 5 in before shelves or wall lining.