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What size shed do I need? Measure the floor space of everything that sits on the floor, add a clear aisle about 3 ft wide, then add wall shelves. For hand tools that is often 4×8 to 6×6, for a push mower 8×8 to 10×10, and for a lawn tractor 12×12 or bigger with a door 72 inches or wider.

The door and the inside size matter as much as the floor area. Below is a size chart matched to what people store, a five-step method you can do with a tape measure and graph paper, and the door widths of our 3DSHEDPLANS plans so you can check the fit before you buy.

Shed size chart: what size shed do I need?

Sheds fall into three rough groups: small sheds hold hand tools, medium sheds hold a push mower and bikes, and large sheds hold a tractor or a workshop. The groups overlap, so go by what you store. The ranges below come from our own plan layouts. They are a starting point, and your gear may need more or less.

What you store Floor area to plan for Common sizes Door to look for Example plans
Hand tools, hoses, potting supplies 30 to 50 sq ft 4×8, 6×6, 4×12 30 in single 4×8 lean-to, 6×6 lean-to
Push mower, wheelbarrow, rakes, a bike 60 to 100 sq ft 8×8, 10×8, 6×10, 10×10 39 in single or 60 in double 6×10 lean-to, 10×8 gable
Lawn tractor plus garden gear 140 to 170 sq ft 10×14, 12×12, 12×14 72 in or wider 12×12 gable, 12×14 lean-to
Tractor, snow blower, bikes and shelving 160 to 200 sq ft 10×16, 12×16 78 to 84 in double 12×16 gable, double door, 10×16 hip roof
Workshop with a bench and power tools 190 to 320 sq ft 12×16, 12×18, 16×20 Walk door, plus a wide door for long stock 12×18 lean-to, 16×20 gable

Floor area is length times width: a 12×16 is 192 sq ft and a 10×12 is 120 sq ft. Two sizes with almost the same area can work very differently. A 10×10 (100 sq ft) and an 8×12 (96 sq ft) are close, but the 8×12 is 2 ft narrower, which changes how a mower parks.

How to work out your shed size in 5 steps

  1. List what goes on the floor. Mower, wheelbarrow, snow blower, bikes, bins, a workbench. Leave out what will hang on walls for now.
  2. Measure each one. Length, width at the widest point, and the height of anything tall. Write the numbers down.
  3. Draw the inside to scale. Use graph paper, one square per foot, and the inside size (see below). Put the biggest item nearest the door and keep a clear path about 3 ft wide from the door to the back wall, so you can reach everything without moving the mower out.
  4. Add the walls. Wall shelves are usually 16 to 24 inches deep. Draw them on the long walls and check the aisle is still clear.
  5. Add room to grow. If the drawing only just fits, go up one size. Going from 10×12 to 10×14 adds about 17 percent more floor and framing, which costs far less now than a second shed later.

Then mark the size on the ground with stakes and string. Stand inside the string and walk the path the mower will take. You will see problems the drawing missed, such as a tree root or a slope at the door.

Inside size vs outside size

A shed’s size is its outside framing size, so the room inside is smaller. With 2×4 studs, each wall is about 3 1/2 inches thick, so a 10×12 shed loses about 7 inches in each direction. That leaves roughly 9 ft 5 in by 11 ft 5 in of floor inside.

Shelves take more. Two walls of 24 inch shelves in a 10 ft wide shed leave about 5 ft 5 in between them. That is a comfortable aisle, but not room to turn a riding mower, so plan from the inside numbers.

What size shed for a riding mower?

A riding mower needs two things: enough floor and a wide enough door.

TractorData’s dimension sheet for the John Deere S120, a common 42 inch lawn tractor, lists it at about 69.7 in long and 55.2 in wide with the mower deck, or 46.5 in wide with the discharge deflector raised. That machine covers about 27 sq ft of floor. Add about 2 ft on one side to step past it and you are using roughly 40 sq ft before shelves or a second machine.

Now the door. A 60 inch rough opening leaves at most about 2 1/2 inches each side for the S120 with the deck on, and less once the door frame and trim are in.

That only works with the deflector raised and a careful driver. For a lawn tractor, a door 72 inches or wider is the practical choice, and 78 to 84 inches is easier still. A 39 inch single door will not take one at all.

Good fits from our range:

  • 12×12 gable shed plan: 144 sq ft and a 78 inch double door. Room for a tractor plus garden gear.
  • 10×16 hip roof shed plan: 160 sq ft and an 84 inch double door, with bikes along the 16 ft wall.
  • 10×12 gable shed plan: 120 sq ft and a 60 inch double door (rough opening). Only for a narrow rider or a push mower, since the finished opening is a few inches narrower than 60.

Plan the ramp too. Measure the rise from the ground to the shed floor at the door, since a skid or block foundation lifts the floor off the ground. For the same rise, a longer ramp is a gentler climb, so leave clear space in front of the door at least as long as the ramp.

What size shed for a workshop, gym or office?

A workshop needs room to work, not just to park. A bench is usually 24 to 30 inches deep, and you want space behind you to stand and walk past.

Long boards need even more. Cross-cutting an 8 ft board on a miter saw needs about 8 ft of support on one side, and ripping one on a table saw needs about the board’s length in front of the blade and behind it. Most shed shops set the saw in line with the big door and open it for long rips. That is why workshop builds usually start around 12×16.

For a home gym, measure each machine with its working space. Concept2 says its RowErg needs a footprint of about 9 ft by 4 ft to leave room during the stroke.

That fits along the length of a 10×12, which is about 11 ft 5 in inside, with the rest of the floor for a rack or mats. A storage-shed floor is framed for stored gear, not for dropped barbells. For heavy lifting, use thick rubber mats at a minimum, and for a serious rack consider a concrete slab or ask a builder to check the floor.

An office or studio needs less floor than a workshop. A desk, chair and a shelf fit in about 8×10 to 10×12. Windows matter more here than size, and you will want power, insulation and a way to heat or cool it. Plan those runs before the inside walls are covered, and check your local permit office, because wiring and a room people use often bring extra rules.

Check the height, not just the floor

Tall items and some uses decide the height. Ladders, kayaks and lumber need length along a wall or space up in the rafters.

Our gable shed plans have walls about 7 ft 10 in tall on most sizes, measured as framing height. Clear headroom under ceiling joists or rafter ties is less, so measure from the plan.

That rules out uses that need a tall clear ceiling, such as overhead presses or a golf simulator. For a simulator, check the maker’s minimum room size first; it may need a custom taller shed rather than a stock plan. A lean-to shed has one tall wall and one short wall, so tall things go on the high side.

Fit the shed to your yard

Leave space around the shed so you can reach every wall for paint and repairs and so air can move behind it. About 2 to 3 ft on each side is a practical working gap. In front, leave room for the doors to swing. Each leaf of a 78 inch double door swings out about 39 inches, plus the ramp.

Before you pick a size right at a limit, check your local permit office. Many towns use floor area, height and distance from the property line to decide whether a shed needs a permit, and an HOA may add its own rules. Our shed permit checklist lists what to ask. If the foundation needs digging, contact Call 811 before you dig so buried lines get marked; the notice period varies by state.

Common mistakes when choosing a shed size

  • Picking a size without a drawing. A size chart is a start, but only your own layout shows whether the aisle works.
  • Forgetting the door. A big shed with a 36 inch door still cannot take a lawn tractor.
  • Measuring the mower without the deck. Deck and discharge chute make it wider. Measure the widest point.
  • No aisle. If you have to pull three things out to reach the fourth, the shed is too small.
  • Sizing for today only. List what you expect to buy in the next few years, like a snow blower or a second bike, and add it to the drawing.

What we checked: mower size from TractorData’s S120 sheet, rower space from Concept2, and every plan door width, floor area and wall height quoted here from our own plan pages.

Plans that fit

Every 3DSHEDPLANS plan is a $19.99 PDF with a material list, step-by-step 3D images and the door and window sizes on the plan page, so you can check your drawing against the real shed. Browse all sizes on the shed plans page, or start here:

Want to see what a plan looks like first? Download the free 10×12 gable shed plan preview PDF. Once you know the size, our shed cost guide shows what each size may cost, and the shed foundation options guide helps you pick the base.

Frequently asked questions

What size shed do I need for a riding mower?

For a lawn tractor with a 42 inch deck, plan on at least 12×12, or a 10×14, with a door 72 inches wide or more. A John Deere S120 is about 55 inches wide with the deck and about 70 inches long, so measure your own machine at its widest point and compare it with the finished door opening.

Is a 10×12 shed big enough?

A 10×12 (120 sq ft) holds a push mower or a narrow rider, bikes, a wheelbarrow and shelving on two walls. It gets tight if you also want a workbench. Draw your gear to scale on the inside size, about 9 ft 5 in by 11 ft 5 in, before you decide.

Should I go one size bigger than I think?

If your drawing only just fits, yes, as long as the yard and budget allow it. Two extra feet of length costs far less now than a second shed later. Check your local permit office first, because floor area often decides whether a shed needs a permit.

How much space do you lose inside a shed?

With 2×4 walls, each wall takes about 3 1/2 inches, so the floor inside is about 7 inches shorter and 7 inches narrower than the outside size. Shelves 16 to 24 inches deep take more, so plan aisles from the inside size.

Shed building guides