Acre Calculator

Acre Calculator

Updated Sep 1, 2026 By Jehan Wadia

Introduction

This acre calculator tells you how big a piece of land is. You can enter simple measurements, or you can draw the land right on a map. Either way, it gives you the size in acres and five other units.

Pick a shape (rectangle, triangle, circle, trapezoid, or right triangle), then type in the length, width, base, height, or radius. You can use feet, meters, yards, miles, and more. If your land is L-shaped or made of a few pieces, just add more sections. The calculator adds them all up for you.

Prefer the map? Search for an address, then click to drop pins along your property line. Three or more pins close the shape and give you the area. No mouse? Type in latitude and longitude instead.

You get the total in acres, hectares, square feet, square meters, square miles, and square kilometers. You also get the perimeter in feet and meters, which helps if you are planning a fence. A step-by-step section shows the math, and a chart compares your land to things like football fields and parking spaces, so the size is easy to picture.

How to Use Our Acre Calculator

Enter your land size by typing measurements or by drawing your lot on the map. The acre calculator gives you the total area in acres, hectares, square feet, square meters, square miles, and square kilometers, plus the perimeter and step-by-step math.

Measurements tab: Pick this tab to find acres from known lengths and widths.

Land Shape: Choose the shape that matches your land: rectangle or square, triangle, right triangle, circle, or trapezoid. The boxes below change to fit the shape you pick.

Length, Width, Base, Height, or Radius: Type each measurement of your lot. Use numbers greater than zero.

Unit menu: Next to each measurement, pick the unit you measured in: inches, feet, yards, centimeters, meters, kilometers, or miles. You can mix units, and the calculator converts them for you.

Add Another Section: Click this to add more shapes for odd lots, like L-shaped or U-shaped land. All sections are added together, and each one shows in the breakdown table. Use the red X to remove a section.

Map tab: Pick this tab to measure real land area on a satellite-style map.

Search box: Type an address, city, or place name and press Search to move the map to your property.

Map clicks: Click each corner of your property to drop boundary pins. After three pins, the shape closes and the acres appear.

Undo Last Pin and Clear All: Use Undo to remove your last pin, or Clear All to start the boundary over.

Latitude and Longitude: If you know exact coordinates, type them in and click Add Pin. This also works if you cannot use a mouse.

Calculate and Reset: Click Calculate to update your results, or Reset to clear everything and start fresh. Use Copy Results to save the acres and perimeter as text.

What Is an Acre?

An acre is a unit used to measure land. One acre equals 43,560 square feet, or about 4,047 square meters. It is the most common way to measure land size in the United States and the United Kingdom.

The acre started as a farming term. It was about how much land one person with one ox could plow in a single day. Today it is a fixed size, not a guess. An acre has no set shape. A square acre is about 208.7 feet on each side, but an acre can be long and thin or wide and short. Only the total space inside matters.

Acre Size Compared to Things You Know

An acre is a little smaller than an American football field, which covers about 1.32 acres including the end zones. It is close to the size of a city block in many towns. You could fit about 16 tennis courts inside one acre. A common home lot in the suburbs is about a quarter acre.

Common Land Area Conversions

1 acre = 43,560 square feet
1 acre = 4,046.86 square meters
1 acre = 0.4047 hectares
1 acre = 4,840 square yards
1 square mile = 640 acres (this is called a "section")
1 hectare = 2.471 acres

How Land Area Is Found

To get the acres of a lot, you first find its area in square feet or square meters, then divide. Each shape uses its own formula:

Rectangle or square: length × width
Triangle: ½ × base × height
Right triangle: ½ × side A × side B
Circle: π × radius²
Trapezoid: ½ × (base 1 + base 2) × height

Once you have the area in square feet, divide by 43,560 to get acres. If your area is in square meters, divide by 4,046.86 instead.

Odd-Shaped Lots

Real land is rarely a neat rectangle. Most lots are L-shaped, U-shaped, or have curved edges. The easy fix is to split the land into simple shapes, find the area of each one, then add them all up. This works for farms, yards, building lots, and pastures.

Why Perimeter Matters

Area tells you how much space is inside. Perimeter tells you how far it is around the edge. You need the perimeter to buy fencing, plan a hedge, mark property lines, or lay a driveway border. Two lots can have the same acreage but very different perimeters, so always check both before buying materials.

Measuring From a Map

You can also measure land by marking corner points on a satellite map. Each point is set by its latitude and longitude, and the distance between points is measured across the curve of the Earth. This method is fast and works well for large fields, wooded land, and lots you cannot walk across. For legal papers, deeds, or building permits, always use a licensed surveyor.

Where Acres Are Used

Acres show up in real estate listings, farm records, tax bills, zoning rules, and timber sales. Farmers use acres to plan seed, fertilizer, and water. Builders use acreage to check lot coverage rules and to size jobs. Homeowners use it for sod, mulch, and lawn care, since most products list coverage per 1,000 square feet or per acre. On the money side, acreage matters when you are valuing a parcel.

Formulas used

Unit conversion of each dimension to meters

L_{m} = L_{unit} \times k_{unit}, \quad k \in \{0.0254,\ 0.3048,\ 0.9144,\ 0.01,\ 1,\ 1000,\ 1609.344\}

Rectangle area and perimeter

A = L \times W, \qquad P = 2(L + W)

Triangle area and perimeter (isosceles assumption)

A = \frac{1}{2} b h, \qquad P = b + 2\sqrt{\left(\frac{b}{2}\right)^2 + h^2}

Right triangle area and perimeter

A = \frac{1}{2} a b, \qquad P = a + b + \sqrt{a^2 + b^2}

Circle area and circumference

A = \pi r^2, \qquad P = 2 \pi r

Trapezoid area and perimeter (isosceles assumption)

A = \frac{b_1 + b_2}{2} h, \qquad P = b_1 + b_2 + 2\sqrt{h^2 + \left(\frac{b_1 - b_2}{2}\right)^2}

Total area and perimeter of all sections

A_{total} = \sum_{i=1}^{n} A_i, \qquad P_{total} = \sum_{i=1}^{n} P_i

Area conversions from square meters

\text{ac} = \frac{A}{4046.8564224},\quad \text{ha} = \frac{A}{10000},\quad \text{ft}^2 = A \times 10.763910416709722,\quad \text{mi}^2 = \frac{A}{2589988.110336}

Geodesic (spherical) polygon area from map pins

A = \left| \frac{R^2}{2} \sum_{i=1}^{n} (\lambda_{i+1} - \lambda_i)\left(2 + \sin\varphi_i + \sin\varphi_{i+1}\right) \right|,\quad R = 6378137\ \text{m}

Great-circle (haversine) edge length and map perimeter

d = 2R\,\arctan\!\left(\frac{\sqrt{a}}{\sqrt{1-a}}\right),\quad a = \sin^2\!\frac{\Delta\varphi}{2} + \cos\varphi_1\cos\varphi_2\sin^2\!\frac{\Delta\lambda}{2},\quad P = \sum_{i=1}^{n} d_i

Frequently asked questions

Do I need to click a pin back on my starting point?

No. The calculator closes the shape for you. After your last pin, it draws a line straight back to pin 1 automatically.

If you do add a pin on top of your first one, it just adds a zero-length edge and does not change the area.

Can I subtract a house, pond, or driveway from my land?

There is no subtract button. Do it in two steps:

Measure the whole lot and write down the acres.
Measure just the pond or building the same way.
Subtract the second number from the first.

How do I measure a round field, like one with a center pivot?

Pick the Circle shape and enter the radius, which is the distance from the middle to the outer edge.

If you only know the distance all the way across (the diameter), divide it by 2 first.

What is a quarter acre in square feet?

A quarter acre is 10,890 square feet. Here are other common sizes:

1/8 acre = 5,445 sq ft
1/4 acre = 10,890 sq ft
1/2 acre = 21,780 sq ft
1 acre = 43,560 sq ft
5 acres = 217,800 sq ft

My lot is 100 feet by 200 feet. How many acres is that?

That is 20,000 square feet. Divide by 43,560 and you get about 0.459 acres, just under half an acre.

Pick Rectangle, type 100 and 200 in feet, and the calculator shows the same answer plus the perimeter.

Why does the triangle perimeter say it assumes an isosceles shape?

A base and a height are enough to find the area, but not enough to know the two slanted sides. Many different triangles share the same base and height.

So the tool picks the balanced (isosceles) version for the perimeter. If you know your exact side lengths, use the Right Triangle shape or measure each side yourself.

Why is the perimeter of my multi-section lot too big?

When you add sections, the tool adds up each shape's full outline. Where two sections touch, that shared inside edge gets counted even though there is no real fence line there.

For fencing, measure only the true outside edges, or use the map tab and pin the outer corners.

Why is my number a little different from Google Earth or my county map?

Small pin differences add up. Zoom levels, satellite image shift, and where exactly you click each corner all change the result.

A difference of a few percent is normal. A big gap usually means a pin landed in the wrong spot, so undo it and try again.

What is the difference between gross and net acres?

Gross acres is everything inside your property lines. Net acres is what is left after you take out roads, easements, wetlands, or steep parts you cannot build on.

This calculator gives gross acres. Check your plat or local rules to find what counts as usable.

Can I measure something other than land, like a lake or a roof?

Yes. The math works for any flat shape. Measure a pond, a pasture, a parking lot, or a garden bed the same way.

Just remember a roof with a slope will measure smaller from above than its real surface.

Rate this calculator