Outdoor & Structure Calculators
Fencing, decking, roofing, stairs, lumber and framing.
A 20 ft wall framed at 16 inches on centre takes 16 studs, and a 1,500 ft² roof is 15 squares of shingles. These nine calculators handle fencing, decking, roofing, stairs, framing and trim, where the answer is a count of standard-length pieces.
All 9 outdoor & structure calculators
Everything here is spacing, not area
The materials calculators elsewhere on this site divide an area by a coverage figure. These do something different: they fit standard-length pieces at a standard spacing into a measured run. That changes the arithmetic in one important way, because you nearly always need one more piece than the division suggests.
A 20 ft wall at 16 in on centre is the clearest example. Twenty feet divided by 16 inches is 15, but the wall needs 16 studs: 15 gaps have 16 ends. Miss that and every fence, deck and stud wall you estimate comes up exactly one short.
The spacings these calculators assume
These are conventional figures, and every one of them can be overridden by your local building code, which wins. Check before you cut anything structural.
| Element | Typical spacing | Where it varies |
|---|---|---|
| Wall studs | 16 in on centre | 24 in for non-load-bearing; 400 or 600 mm metric |
| Deck joists | 16 in on centre | 12 in for diagonal decking or heavier loads |
| Fence posts | 6 to 8 ft apart | Panel width decides it; metric panels are 1.83 m |
| Stair risers | 7 to 7 3/4 in | Code sets a maximum, and all risers must be equal |
| Roofing | Sold by the square, 100 ft² | Three bundles per square for most shingles |
Roofing has a second step the others do not: your roof area is bigger than the footprint it covers, because it slopes. A pitch multiplier has to be applied to the footprint before you count squares, and on a steep roof the difference is well over 10%.
Waste on linear materials behaves differently
On a floor, waste is a percentage because the cuts are spread over an area. On linear material it is lumpy: a 14 ft run cut from 16 ft boards wastes 2 ft from each one, which is 12.5%, while the same run from 8 ft boards wastes nothing at all but adds a joint. That is why board length is a real decision rather than a detail, and why the deck, fence and trim calculators ask for it.
Trim is the sharpest case. Baseboard and crown moulding are mitred at corners, so each corner consumes length, and a room with many corners needs noticeably more than its bare perimeter. Buying the next length up is usually cheaper than joining two shorter pieces in the middle of a visible wall.
Board feet are a volume, not a length
One calculator here answers a different question entirely. A board foot is a unit of volume used to price hardwood: 144 cubic inches, or a piece 1 ft × 1 ft × 1 in. Hardwood is sold this way because boards come in random widths, so a price per linear foot would be meaningless. If you are buying rough lumber, note that it is normally measured at its rough thickness before surfacing, so you pay for wood the planer removes.
Outdoor & Structure Calculators: common questions
How many studs do I need for a 20 ft wall?
16 at 16 inches on centre. The division gives 15 spaces, and a wall needs one stud at each end of every space, so it is always spaces plus one. Corners and openings add more on top of that.
What is a square of roofing?
100 square feet of roof surface, which is how shingles are sold. Most architectural shingles run three bundles to the square. Apply the pitch multiplier first, since a sloped roof is larger than the footprint beneath it.
How far apart should fence posts be?
6 to 8 feet for most residential fencing, and in practice the panel width decides it. Metric panels are normally 1.83 m wide. Closer spacing is stronger and costs more in both posts and concrete.
Does board length affect how much decking I need?
Considerably. A 14 ft run cut from 16 ft boards wastes 2 ft off each, about 12.5%, while 8 ft boards would waste none but add a joint. The deck board calculator takes board length because it changes the order.