Area

British Area

1 sq foot = 144 sq inches
1 sq yard = 9 sq feet
1 sq rod = 30.25 sq yards
1 sq chain = 16 sq rods
1 rood = 2.5 sq chains
1 acre = 4 roods
1 acre = 160 sq rods
1 acre = 4840 sq yards
1 sq mile = 640 acres
1 sq mile = 1 section
1 township = 36 sections
U.S. Area

1 sq foot = 144 sq inches
1 sq yard = 9 sq feet
1 sq rod = 30.25 sq yards
1 acre = 160 sq rods
1 sq mile = 640 acres
1 sq mile = 1 section
1 township = 36 sections
1 township = 6 miles square
Geometric Figures

Square -- square of a side (A = s²)
Rectangle -- length times width (A = l x w)
Circle -- pi times radius squared (A = 3.1416 x r²)
Triangle -- one-half times base times height (A = 1/2 x b x h)
Trapezoid -- one half times sum of the two parallel sides times height (A = 1/2 x [parallel side 1 + parallel side 2] x h)
Parellogram -- base times height (A = b x h)
Lateral Surface of a Cylinder -- two times pi times radius times height (A = 2 x 3.1416 x r x h)
End Surface of a Cylinder -- two times pi times radius squared (A = 2 x 3.1416 x r ²)
Total Surface of a Cylinder --
lateral area plus end areas (A = [2 x 3.1416 x r x h] + [2 x 3.1416 x r ²]

Lateral Surface of a Cone -- pi times radius times slant height (A = 3.1416 x sh)
End Surface of a Cone -- pi times radius squared (A = 3.1416 x r²)
Total Surface of a Cone -- lateral area plus end areas (A = [3.1416 x sh] + {3.1416 x r²}
Surface of a Sphere -- four times pi times radius squared (A = 4 x 3.1416 x r²)
Metric

10,000 sq. metres = 1 are
100 ares = 1 hectare