How to measure your shed or building

Length, width and height for garden buildings. Span, length and eaves height for farm and steel buildings. Here's how to measure each one so builders quote for the same thing.

Updated 2026-10-06

Builders and suppliers price from three numbers. Give them the right three, in the right order, and the quotes you get back will be for the building you actually want.

Measuring a garden shed, garden room or workshop

• Length is the longest side of the building.
• Width is the other side, measured front to back. Some sellers call this the depth.
• Height is from the ground to the highest point of the roof (the ridge on an apex shed). The eaves height is lower: it is where the roof meets the walls.

When a shed is sold as a "10×8", most UK suppliers mean 10 ft long by 8 ft wide. Not all do, so check which side the door is on before you order.

Step by step

1. Measure the space, not the shed. Use a tape to measure the area you have, wall to wall or fence to fence, in both directions.
2. Take off 60 cm (2 ft) on every side. You need room to put the panels up, treat the timber and walk round it. That gives you the biggest shed that fits.
3. Mark it out. Put pegs and string where the corners would go. Stand back and check doors open, paths are clear and windows aren't blocked.
4. Decide the height. If the shed will be within 2 m of a fence or boundary, keep the overall height to 2.5 m or less in England to stay within permitted development. See our planning guide.
5. Note the door side and any slope. Say which long or short side you want the door on, and whether the ground slopes, because it changes the base.
6. Enter length, width and height on the quote form, choosing feet or metres.

Internal, external or base size?

Suppliers sometimes quote the nominal size, which can be a few centimetres different from the real external size, especially once the roof overhang is added. The base usually needs to match the floor size of the shed, not the roof. If space is tight, ask each supplier for the external footprint including the roof.

Measuring an agricultural or steel frame building

• Span is the clear width of the building, measured between the steel columns. This is the number that most affects the size and cost of the steel.
• Length is the building from end to end. It's usually a number of bays: for example, 5 bays of 6 m is 30 m long.
• Eaves height is from the floor to the top of the side wall, where the roof starts. It decides what machinery fits inside.
• Ridge height is the highest point of the roof. Contractors work it out from the span, eaves and roof pitch, so you don't need to give it.

Step by step

1. Start with what goes inside. Measure the machinery, the number of bales, or the pens you need. That sets the span and length.
2. Check the clearance you need. A tipping trailer or telehandler at full reach needs much more height than a tractor. Measure the tallest thing that will go in, then add a margin. Machinery stores often need 5 m or more at the eaves.
3. Pick the span. Allow room to turn and open doors. Common spans for farm buildings run from about 12 m to 30 m.
4. Work out the length in bays. Decide how many bays you need. Bays are often 4.8 m to 6 m wide, so the contractor can advise.
5. Measure the site. Check the space you have, access for a lorry and crane, and the distance to roads and houses, which matters for planning.
6. Enter span, length and eaves height on the quote form. The form switches to these labels when you pick an agricultural or steel building.

Quick checklist before you ask for quotes

Feet or metres?

Use whichever you're comfortable with. Garden sheds are still mostly sold in feet, while farm and steel buildings are designed in metres. To convert, 1 foot is 0.3048 metres, so a 10×8 ft shed is about 3.05 × 2.44 m, and 1 metre is about 3 ft 3 in.

Questions