Plot Area Calculator

This calculator is built for a building plot rather than a field. Alongside the area in square feet, square metres, square yards, marla, kanal, acres and hectares, it returns the perimeter — the total run along the edges of the plot, which is the number you need before you can price a boundary wall, a fence or the foundation strip.

Plots are rarely perfect rectangles. Tick the box for a plot that narrows or widens at one end and the calculator switches to the trapezoid formula, measuring the sloping side properly instead of averaging the two widths and hoping the error is small.

Why the perimeter matters as much as the area

Two plots with the same area can have very different perimeters. A 50 × 90 foot plot and a 30 × 150 foot plot are both 4,500 square feet, but the first has a perimeter of 280 feet and the second 360 feet. If you are building a boundary wall at a cost per running foot, the narrow long plot costs nearly 30% more to enclose for exactly the same land area.

Perimeter also drives the foundation and damp-proof course for the wall, the number of gate piers, and how much of the plot is lost to the wall's own footprint — which matters when local rules cap how much of the plot you may cover.

Measuring a plot that is not rectangular

Stand at the road and measure the frontage. Then walk to the back and measure the rear width. Measure the depth along the side boundary — the perpendicular distance between the front and rear lines, not the distance along the sloping side. Enter those three figures, tick the irregular box, and the calculator applies the trapezoid formula.

For a plot with a cut corner, or one boundary that runs at an angle, the practical approach is to split the plot into a rectangle plus a triangle on paper, work out each shape here, and add the two areas. It takes an extra minute and gives a figure you can defend.

Worked example

A plot measures 50 feet wide by 90 feet deep. The area is 4,500 square feet — 16.53 marla at the traditional standard, 18 marla at 250 square feet, 0.827 kanal, and 0.1033 acres. The perimeter is 280 feet, so a boundary wall in blockwork needs 280 running feet of wall plus gate piers.

Now suppose the same plot is 50 feet at the front and 44 feet at the back, still 90 feet deep. It becomes a trapezoid: ½ × (50 + 44) × 90 = 4,230 square feet, or 15.54 marla — about 6% less land than the rectangle it looked like on the plan. The sloping side is measured as a true diagonal, giving a perimeter of 279.8 feet.

Area, covered area and local byelaws

Almost everywhere, the permitted covered area is set as a fraction of the plot area — a floor area ratio or coverage limit. That makes the figure you calculate here the input to a planning question, not just a pricing question. Compute the area first, then check your local authority's table for the maximum ground coverage and the maximum total floor area, because those limits are usually expressed as a percentage of exactly this number.