How this instrument works
Square footage is the currency of home and garden projects: sod, tile, laminate flooring, and shingles are all priced, packaged, and delivered by the square foot, so a triangular section of a yard, room, or roof needs its area expressed in exactly that unit before a supplier can quote it. This sheet runs the ordinary A = ½ × base × height relation but keeps Base and Height pinned to feet by default, so whatever lands in the Area field is already the number a materials order needs, with no conversion pass tacked on afterward.
Picture the triangle sitting inside a rectangle built from its base and a matching upright side: slide a duplicate triangle, flipped, against the first and the pair tiles neatly into a parallelogram with that same base and upright measurement, area base-times-upright by plain multiplication. One triangle is exactly half of that shape, no matter whether it leans acute, obtuse, or square at one corner. That upright measurement, entered as Height, has to rise square to the base rather than run along a slanted edge — a tape laid along a leaning fence rail or a raked roofline reads longer than the true upright gap and quietly inflates every square-foot figure that follows.
Shrink Height toward nothing and the triangle collapses flat onto its own base line, the Area field sliding smoothly down to zero with it — no special branch needed anywhere in the arithmetic. A separate trap waits in the unit menus rather than the geometry: one square yard holds nine square feet, not three, since a two-dimensional figure moves with the square of any length change, not the change itself. Switching Base and Height's own dropdowns handles that squaring automatically, which is safer than converting a finished square-foot answer by hand afterward.
- Enter the triangle's base — the edge you measured along, such as a fence line, wall, or roof eave — into the Base field, choosing ft, in, yd, or m from its unit menu.
- Enter the upright gap between that base line and the far corner into the Height field, keeping it square to Base rather than along a leaning edge; Height carries its own unit menu, independent of Base's.
- The Area field fills in ½ × Base × Height on its own, defaulting to square feet so it lines up with how sod, tile, and shingles are sold; switch it to yd² or m² without retyping either input.
- If Area shows a warning, check Base and Height for a zero or blank entry — a real triangular section needs a positive length on both sides.
Worked example — a 10-by-6-foot triangular lawn corner
A diagonal fence line cuts off a triangular corner of a backyard, leaving bare dirt that needs new sod. The fence itself is the base, measuring 10 feet, and the perpendicular distance from that fence line back to the true corner post is 6 feet. Area = ½ × 10 × 6 = 30 square feet, the exact figure a sod supplier needs, since turf is cut and priced by the square foot rather than by an abstract, unitless area.
Sod commonly ships in rolls sized 2 feet by 3 feet, six square feet to a roll: a 30-square-foot corner like this one needs exactly five rolls, with nothing left over and no fractional roll to trim. That is the real payoff of working in square feet from the start — the area figure converts directly into a purchase quantity, instead of leaving the ordering decision to guesswork.
Questions
Why does this calculator give the area in square feet instead of a generic unit?
Because that is the unit the materials trade actually uses: sod, tile, laminate flooring, mulch, and roofing shingles are all quoted and packaged by the square foot. Setting Base and Height to feet by default means the Area field already reads out in the unit a supplier's quote will use, with no separate conversion between the geometry and the order form.
Where does this square-footage figure usually go wrong on site?
In how Height gets measured. It has to rise square to the base, not follow a diagonal edge — on site that means checking it with a framing square or a plumb line dropped from the base, rather than reading a tape laid along a leaning fence rail or roofline, which is always longer than the true upright gap and overstates the square footage that follows.
How do I get square yards or square meters instead of square feet?
Use the Area field's own unit dropdown rather than converting the number by hand, because a two-dimensional figure moves with the square of any length change, not the change itself. One square yard holds nine square feet, and one square metre holds about 10.76 square feet — dividing by 3, or multiplying by 3.28, instead of squaring those factors first, is where a hand conversion typically goes wrong.
Does this formula work for a triangular room or roof section, not just a yard?
Yes — base times height over two holds for any triangle regardless of what it represents, so the same Base and Height fields apply to a triangular closet nook, a gable-end roof plane, or a wedge-shaped garden bed. The only requirement is that Height stays perpendicular to whichever edge is chosen as Base; the physical setting changes nothing about the arithmetic.
Should I order extra material to cover waste when a section is triangular?
Many installers pad a straight square-footage figure by roughly ten percent when the section being covered is triangular, since angled cuts at the diagonal edge produce more unusable offcuts than a simple rectangle does. That allowance is a trade rule of thumb rather than part of the geometry — this calculator's Area field reports the true enclosed area, and adding a cutting margin is a separate, deliberate step.