Field Area Calculator
Whether you are working out seed for a paddock, turf for a lawn, or the size of a lot on a listing, field area always comes down to the same step: measure the shape, apply the right formula, and convert to the unit people actually use, acres or hectares. The calculator below handles five shapes (rectangle, square, circle, triangle and trapezoid) in feet or meters, and reports the area in square feet, square meters, acres and hectares in one pass.
1 acre = 43,560 ft² = 4,046.8564224 m². 1 hectare = 10,000 m². Conversions use the standard factors shown in the formula section; the metre-to-square-feet factor is rounded at seven decimals.
Quick Answer
A rectangular paddock of 200 ft by 150 ft is 30,000.00 ft², which is 2,787.09 m², 0.688705 acres and 0.278709 hectares: a little over two-thirds of an acre. The calculator is pre-filled with that field, and every other shape below is pre-filled with its own check example, so each formula in this article can be reproduced with one click.
Key takeaways
- Shape first, units second: pick the shape that matches the field, enter dimensions in feet or meters, and all four area units come back together. No second conversion run.
- The square-feet result line shows the formula with your numbers in it (for example “200 × 150 ft”), so you can audit the arithmetic at a glance.
- Acres and hectares are reported to six decimals because the conversion is exact; your tape measurement is not. Treat the last decimals as conversion precision, not measurement precision.
- Irregular fields are not a dead end: split them into rectangles, triangles and trapezoids, calculate each piece, and add the areas.
How to use the Field Area Calculator
Select a shape, confirm the unit, and calculate. Each shape only asks for the dimensions its formula needs, and the results stay hidden until you click Calculate area.
- Select the shape that best matches your field: rectangle for most paddocks and lots, square for equal sides, circle for centre-pivot irrigation plots, triangle for corner plots, and trapezoid for fields whose two ends have different lengths.
- Choose feet or meters: whichever you measured in. Every dimension must be in that one unit; mixing feet and meters inside one calculation is the most common way to get a nonsense area.
- Enter the dimensions: the form swaps to exactly the fields the shape needs. Heights for triangles and trapezoids must be perpendicular distances, a point the tooltips repeat because it is where hand measurements most often go wrong.
- Read all four units together: square feet and square meters for materials and listings, acres and hectares for farm planning. Reset restores the worked examples if you want to start over.
This page is built around measured shapes: you bring the dimensions. If your starting point is a parcel on a map rather than a tape measurement, the acreage calculator covers that acreage-first route, and the two pages agree on the conversion constants so the numbers line up.
The five formulas and the conversions
Each shape has one formula, and every result then passes through the same three conversions. Nothing else is happening inside the tool, which is what makes it easy to check by hand.
| Shape | Formula | You measure |
|---|---|---|
| Rectangle | Area = Length × Width | Two adjacent sides |
| Square | Area = Side² | One side |
| Circle | Area = π × Radius² | Centre to edge (halve a diameter) |
| Triangle | Area = ½ × Base × Height | A base and its perpendicular height |
| Trapezoid | Area = ((Side A + Side B) ÷ 2) × Height | Both parallel sides and the distance between them |
Conversions: acres = ft² ÷ 43,560; hectares = m² ÷ 10,000; 1 ft² = 0.09290304 m², the exact square of the international foot definition maintained in the SI Brochure published by the Bureau International des Poids et Mesures (BIPM). The acre's definition as 43,560 square feet (one chain by one furlong) is the historical unit described in Britannica's entry on the acre. One honest footnote: when you enter meters, the tool converts square meters to square feet with the factor 10.7639104, a seven-decimal rounding of the exact reciprocal, so meter-based results can differ from a full-precision conversion in about the ninth significant figure. It will never move a seed or fencing decision.
Worked examples: a paddock and a tapering field
Rectangle. A paddock measures 200 ft by 150 ft. Area = 200 × 150 = 30,000.00 ft² = 30,000 × 0.09290304 = 2,787.09 m² = 30,000 ÷ 43,560 = 0.688705 acres = 0.278709 hectares. That is a little over two-thirds of an acre, useful context when a seed bag covers “up to 1 acre.”
Trapezoid. A field with parallel sides of 120 ft and 80 ft, 60 ft apart. Area = ((120 + 80) ÷ 2) × 60 = 6,000.00 ft² = 557.42 m² = 0.137741 acres = 0.055742 hectares. Both examples are the pre-filled values in the calculator, and the remaining three shapes check out the same way:
| Check run | Square feet | Square meters | Acres | Hectares |
|---|---|---|---|---|
| Square, side 100 ft | 10,000.00 | 929.03 | 0.229568 | 0.092903 |
| Circle, radius 50 ft | 7,853.98 | 729.66 | 0.180303 | 0.072966 |
| Triangle, base 120 ft, height 80 ft | 4,800.00 | 445.93 | 0.110193 | 0.044593 |
| Rectangle, 100 m × 75 m | 80,729.33 | 7,500.00 | 1.853290 | 0.750000 |
Irregular fields, slopes and what to do with the number
Most real fields are not one clean shape. Split them: a rectangle for the main body, a triangle for the corner the road cuts off, a trapezoid where the far end tapers, then add the three areas. For curved boundaries, a GPS walk or a phone planimeter app traces the edge directly; the USDA Web Soil Survey is the reference many US landowners use to cross-check parcel areas against soil-mapping data.
Worked split: take the paddock above (rectangle, 0.688705 acres) and add the triangular corner plot from the checks table (base 120 ft, height 80 ft, 0.110193 acres). Run each shape on its own, then add: 30,000.00 + 4,800.00 = 34,800.00 ft², and 0.688705 + 0.110193 = 0.798898 acres for the whole field. Keep each piece in the same unit before adding, and round only at the end; adding the six-decimal acre figures piece by piece is more accurate than adding rounded square-feet figures.
Once the area is settled, it usually feeds a cost question. Seed, feed and input budgets scale with acreage, so a figure like the corn cost per acre calculator turns this page's acres into a per-acre cost, and the broader cost per acre calculator does the same for any per-acre expense. Fencing runs the other way: it prices the boundary, not the surface, so pair the area here with the fence price calculator once you have measured the edges you already walked for this calculation. On sloped ground, remember the tape follows the slope while maps and legal areas are plan-view; the difference is small under about 5 degrees and grows quickly after that.
What competing calculators miss
The field and farm area keyword splits into camps, and each camp makes you do one extra job:
- AcreageCalculator.net: the widest rival, with six shapes including an ellipse and a known-area direct entry, seven input units, a perimeter estimate and shape diagrams. The cost of that breadth is an acres-first flow; a metric user measuring a trapezoid still lands on a page organised around square feet.
- CalculatorsHub Farm Area: built for farms split into sections, with a sensible sum-the-sections method and a common-values table. As a quick single-field check it is heavier than it needs to be, and its worked examples lean on conversion tables instead of showing the formula inside the result.
- Softonic's multi-parcel acreage tool: an auditable section-by-section breakdown and an unusually honest survey disclaimer, but the teaching around the formulas is thin; you get a total, not an understanding.
- ConstructlyTools: generous input units (yards, chains and miles alongside feet and meters) and an optional price-per-acre line. Its core shape set is narrower, and the trapezoid that real tapering fields need is not its focus.
- Mappr and the map-tracing tools: drawing on satellite imagery is excellent when the boundary is visible from above and useless when it is under tree cover or you only have tape measurements from the ground.
- The gap this page fills: five measured shapes including the trapezoid, feet or meters in, four units out in one pass, the formula printed inside the square-feet result with your own numbers substituted, and inline validation that names the missing field instead of a popup or a silent NaN.
Frequently asked questions
Divide it into rectangles, triangles, and trapezoids, measure each, and add the areas. For curved boundaries, GPS track loggers and phone-based planimeter apps trace the boundary and compute the area directly.
Use what your audience uses: acres are standard in the US, UK, and much of South Asia; hectares are standard across most of the metric world. The calculator reports both, so the choice never blocks you.
No. It is fine for planning seed, fencing materials, and listings, but legal boundaries, disputes, and registered titles need a licensed surveyor's work.
Usually within a few percent for simple shapes, which is plenty for input planning. Slopes inflate plan-view tape readings slightly; for hilly ground, GPS area tracing is more honest.
Multiply the product's per-acre rate by your acres: a 50 lb bag rated at 25 lb per acre covers 2 acres, so 0.688705 acres needs about 17.22 lb. Always check the label rate for your specific crop.
Yes. The same shapes and conversions apply; for small plots the square-feet and square-meter readouts are usually the useful ones.
Add This Calculator to Your Website
Embed this calculator on your own site with the code below. Pick a size to preview it live, then copy the code.
Powered by Calculator Zilo
References
- Bureau International des Poids et Mesures (BIPM). The International System of Units (SI Brochure). Accessed October 21, 2026.
- National Institute of Standards and Technology. Guide for the Use of the International System of Units (SI). Accessed October 21, 2026.
- Weisstein, Eric W., Wolfram MathWorld. Area. Accessed October 21, 2026.
- Weisstein, Eric W., Wolfram MathWorld. Trapezoid. Accessed October 21, 2026.
- Encyclopaedia Britannica. Acre (unit of measurement). Accessed October 21, 2026.
- USDA Natural Resources Conservation Service. Web Soil Survey. Accessed October 21, 2026.