Triangle Area Calculator
Find the area of any triangle from base & height, three sides (Heron's formula), or two sides and the included angle. Get all sides, angles, perimeter and a to-scale drawing — ideal for triangular lots and parcels.
Area = ½ × base × height.
If the triangle is a land parcel, enter a price per acre to estimate its value.
| Unit | Value |
|---|---|
| Calculate to see all conversions | |
How to use the triangle area calculator
Four quick steps turn whatever you measured into area — plus every side, every angle, the perimeter, acres, an estimated land value, and a downloadable PDF.
Pick what you know
Base and height, all three sides, or two sides with the angle between them.
Enter your measurements
Work in feet, yards, or meters — switching the unit re-reads every dimension.
Add a price per acre
Optional. If the triangle is a parcel, this turns the area into an estimated value.
Read results & save a PDF
Area, sides, angles, perimeter, conversions, and a to-scale drawing of your triangle.
How triangle area is calculated
Three routes lead to the same answer, and which one you take depends entirely on what you were able to measure. Once the area is known, the law of cosines fills in the sides and angles you didn’t enter. Here is the exact math.
Worked example — a triangle with a 100 ft base and an 80 ft height
Area: ½ × 100 × 80 = 4,000 sq ft
Acres: 4,000 ÷ 43,560 = 0.092 acres
Square meters: 4,000 × 0.092903 = 371.6 sq m
Equal sides (symmetric apex): √(50² + 80²) = 94.34 ft
Perimeter: 100 + 94.34 + 94.34 = 288.68 ft
Base angles: arctan(80 ÷ 50) = 58.0°, apex 180 − 116.0 = 64.0°
≈ 4,000 sq ft, 0.092 acres, isosceles and acute.
All three describe the same 0.055-acre triangle with a 240 ft perimeter. Pick the method that matches your measurements rather than the one that looks simplest — converting between them by hand is where errors creep in.
Triangle area & geometry charts
The lookups that come up when measuring a triangle — common dimensions, how to name the shape you’ve got, which method fits your measurements, and the unit conversions behind it all.
| Base × height | Area | Acres | Square meters |
|---|---|---|---|
| 20 × 15 ft | 150 sq ft | 0.003 ac | 13.9 sq m |
| 40 × 30 ft | 600 sq ft | 0.014 ac | 55.7 sq m |
| 60 × 40 ft | 1,200 sq ft | 0.028 ac | 111.5 sq m |
| 80 × 60 ft | 2,400 sq ft | 0.055 ac | 223.0 sq m |
| 100 × 80 ft | 4,000 sq ft | 0.092 ac | 371.6 sq m |
| 150 × 120 ft | 9,000 sq ft | 0.207 ac | 836.1 sq m |
| 200 × 150 ft | 15,000 sq ft | 0.344 ac | 1,393.5 sq m |
| 330 × 264 ft | 43,560 sq ft | 1.000 ac | 4,046.9 sq m |
A triangle always covers exactly half of the rectangle that shares its base and height — which is why a wedge-shaped parcel holds far less land than its street frontage suggests.
| What you know | Method | Formula |
|---|---|---|
| Base and perpendicular height | Base & height | ½ × b × h |
| All three side lengths | Three sides (Heron) | √(s(s−a)(s−b)(s−c)) |
| Two sides and the angle between | Two sides + angle | ½ × a × b × sin(C) |
| Two sides and a right angle | Two sides + angle | ½ × leg × leg |
| Three corner coordinates | Derive the sides first | Shoelace, then Heron |
| Two sides, angle not between them | Not enough — ambiguous | Measure the third side |
The last row is the classic trap: an angle that sits opposite one of your sides rather than between them can describe two different triangles with two different areas.
| Type | Condition | What it means in practice |
|---|---|---|
| Equilateral | All three sides equal | Every angle is exactly 60° |
| Isosceles | Two sides equal | The two base angles match |
| Scalene | All sides different | All three angles differ — most real parcels |
| Right | One angle is 90° | The two legs are the base and the height |
| Acute | Every angle under 90° | Altitude always lands inside the base |
| Obtuse | One angle over 90° | Altitude falls outside the base line |
The calculator names your triangle on both counts at once — “Scalene · Obtuse”, for instance — using the sides and angles it solved for.
| Convert | Multiply / divide | Where it’s used |
|---|---|---|
| Sq ft → acres | ÷ 43,560 | US land and parcel sizing |
| Sq ft → sq m | × 0.092903 | Metric site plans |
| Sq m → sq ft | × 10.764 | Reading an overseas listing |
| Sq ft → sq yd | ÷ 9 | Older deeds, sod and paving quotes |
| Acres → hectares | × 0.4047 | Quoting a US parcel abroad |
| $ per acre → $ per sq ft | ÷ 43,560 | Comparing land and lot pricing |
Match the price basis to the area unit before comparing rates — rural land is usually quoted per acre, suburban lots per square foot.
| Area | Acres | Rough comparison |
|---|---|---|
| 400 sq ft | 0.009 ac | A one-car garage floor |
| 2,788 sq ft | 0.064 ac | One tennis court |
| 4,704 sq ft | 0.108 ac | One basketball court |
| 10,890 sq ft | 0.250 ac | Quarter-acre lot |
| 43,560 sq ft | 1.000 ac | One acre |
| 57,499 sq ft | 1.320 ac | An American football field |
The calculator shows the same comparison live — football fields, basketball courts, and tennis courts — as you change the dimensions.
The base is whichever side you measure from, and the height is the perpendicular drop from the opposite corner onto it — which is why the height is almost never the length of a slanted side.
- Any two sides must beat the third — 30, 40, and 80 ft can’t close into a triangle, and the calculator will say so rather than guess.
- Base and height fix the area, not the shape — countless triangles share the same pair, so the drawing assumes a symmetric apex over the base.
- Obtuse triangles push the height outside — the altitude lands on an extension of the base, so measure it from the corner straight down, not along the ground between the stakes.
Everything the calculator works out
One set of measurements gives you the full picture — the area in every unit, the sides and angles you didn’t enter, what the land is worth, and a drawing you can hand to someone else.
The figures behind every triangle calculation
Built for anyone measuring an odd-shaped space
A wedge-shaped parcel, a gable end, a corner of the yard that won’t square up — the same three measurements answer all of them.
Working out how much usable ground a triangular or corner parcel really holds, and what the asking price comes to per acre.
- Use the side lengths straight off the plat
- Compare acres against the listing
- Price it per acre before you offer
Sizing sod, gravel, mulch, decking, or the shingles on a gable end without over-ordering for a shape that isn’t square.
- Measure the height perpendicular, not along the slope
- Add your own waste factor on top
- Save the PDF with the quote
Sanity-checking a listed acreage on an irregular lot, or quoting a wedge parcel accurately before the survey comes back.
- Quote both sq ft and acres
- Split irregular lots into triangles
- Flag anything the plat contradicts
7 tips for measuring a triangle accurately
Small habits that keep a triangle estimate honest — and stop a mis-measured height from throwing the whole area out.
Triangle area calculator FAQ
The area, formula, and land measurement questions people ask most when a shape refuses to be a rectangle.
Multiply the base by the perpendicular height and halve it. A triangle with a 100 ft base and an 80 ft height is 4,000 sq ft, or about 0.092 acres.
The height has to be measured at a right angle to the base, not along a slanted side. If you only know the three side lengths, use Heron’s formula instead; if you know two sides and the angle between them, use ½ × a × b × sin(C).
Heron’s formula finds the area from three side lengths alone, with no height or angle needed. First take the semi-perimeter s = (a + b + c) ÷ 2, then area = √(s(s−a)(s−b)(s−c)).
For sides of 50, 60, and 70 feet, s is 90 and the area works out to about 1,469.7 sq ft. This is the method to use for a surveyed parcel, where the deed lists boundary lengths but no interior height.
Use area = ½ × a × b × sin(C), where C is the angle sitting between the two sides you measured. Two sides of 60 and 80 feet with a 50° angle between them give 1,838.5 sq ft.
The angle must be the included one. If your angle is opposite one of the sides rather than between them, the triangle isn’t uniquely defined and two different shapes can fit the same measurements.
The height, or altitude, is the perpendicular distance from the base to the opposite corner. It is not the length of a slanted side, which is the most common measuring mistake.
If you already know the area and the base, work backwards: height = 2 × area ÷ base. On a triangle of 50, 60, and 70 feet measured against the 70 ft side, the altitude comes to about 42.0 feet.
Work out the area in square feet, then divide by 43,560. A triangular parcel with a 300 ft base and a 200 ft depth is 30,000 square feet, which is 0.689 acres.
A triangle covers exactly half the ground of a rectangle with the same base and depth, which is why corner and wedge parcels usually hold less usable land than their street frontage suggests.
No. Any two sides added together have to be longer than the third, which is called the triangle inequality. Lengths of 30, 40, and 80 feet cannot close, because 30 + 40 = 70.
When the calculator reports that the figure is not a valid triangle, this rule is almost always the reason. Re-check the longest measurement first — a single transposed digit there breaks the whole set.
Use the shoelace formula: |x₁(y₂−y₃) + x₂(y₃−y₁) + x₃(y₁−y₂)| ÷ 2. Corners at (0,0), (100,0), and (40,80) give 4,000 sq ft.
If you are working from a plat or a GPS trace, you can also measure the three side lengths from the coordinates and enter them under the three sides method, which gives the same answer.
No. This is a planning estimate calculated from the dimensions you enter, treating the parcel as a perfect triangle with straight sides. It doesn’t know your jurisdiction’s zoning, easements, right-of-way, or floodplain, and it can’t account for curved or jogged boundaries.
For a permit application, a deed, a mortgage, or a boundary dispute you need the recorded plat and a licensed surveyor. Use this to size up a parcel before that stage.
Not a Survey — Planning Estimate Only: This calculator computes area, side lengths, interior angles, perimeter, and unit conversions from the dimensions you enter, treating the shape as an idealized triangle with perfectly straight sides. Actual boundaries are established only by a licensed surveyor and the recorded plat or legal description, and results here carry no legal standing for permitting, deeds, financing, boundary disputes, or subdivision. Where you enter only a base and a height, the area is exact but the sides and angles shown assume a symmetric apex over the base — enter three sides if the true outline matters. Land value is a simple rate multiplication and is not an appraisal; access, utilities, zoning, topography, and frontage materially affect real market value. For planning purposes only.