The following is a list of significant formulae involving the mathematical constant . Many of these formulae can be found in the article Pi, or the article Approximations of .
Euclidean geometry
where is the circumference of a circle, is the diameter, and is the radius. More generally,
where and are, respectively, the perimeter and the width of any curve of constant width.
where is the area of a circle. More generally,
where is the area enclosed by an ellipse with semi-major axis and semi-minor axis .
where is the area between the witch of Agnesi and its asymptotic line; is the radius of the defining circle.
where is the area of a squircle with minor radius , is the gamma function and is the arithmetic–geometric mean.
where is the area of an epicycloid with the smaller circle of radius and the larger circle of radius (), assuming the initial point lies on the larger circle.
where is the area of a rose with angular frequency () and amplitude .
where is the perimeter of the lemniscate of Bernoulli with focal distance .
where is the volume of a sphere and is the radius.
where is the surface area of a sphere and is the radius.
where is the hypervolume of a 3-sphere and is the radius.
where is the surface volume of a 3-sphere and is the radius.
Regular convex polygons
Sum of internal angles of a regular convex polygon with sides:
Area of a regular convex polygon with sides and side length :
Inradius of a regular convex polygon with sides and side length :
Circumradius of a regular convex polygon with sides and side length :
Physics
The cosmological constant:
Heisenberg's uncertainty principle:
Einstein's field equation of general relativity:
Coulomb's law for the electric force in vacuum:
Magnetic permeability of free space:
Approximate period of a simple pendulum with small amplitude:
Exact period of a simple pendulum with amplitude ( is the arithmetic–geometric mean):
Kepler's third law of planetary motion:
The buckling formula:
A puzzle involving "colliding billiard balls":
is the number of collisions made (in ideal conditions, perfectly elastic with no friction) by an object of mass m initially at rest between a fixed wall and another object of mass b2Nm, when struck by the other object. (This gives the digits of π in base b up to N digits past the radix point.)
Formulae yielding
Integrals
(integrating two halves to obtain the area of the unit circle)
(see also Cauchy distribution)
(see Gaussian integral).
(when the path of integration winds once counterclockwise around 0. See also Cauchy's integral formula).
(see also Proof that 22/7 exceeds ).
(where is the arithmetic–geometric mean; see also elliptic integral)
Note that with symmetric integrands , formulas of the form can also be translated to formulas .
Efficient infinite series
(see also Double factorial)
(see Chudnovsky algorithm)
(see Srinivasa Ramanujan, Ramanujan–Sato series)
The following are efficient for calculating arbitrary binary digits of :
(see Bailey–Borwein–Plouffe formula)
Plouffe's series for calculating arbitrary decimal digits of :
Other infinite series
(see also Basel problem and Riemann zeta function)
, where B2n is a Bernoulli number.
(see Leibniz formula for pi)
(Newton, Second Letter to Oldenburg, 1676)
(Madhava series)
In general,
where is the th Euler number.
(see Gregory coefficients)
(where is the rising factorial)
(Nilakantha series)
(where is the n-th Fibonacci number)
(where is the number of prime factors of the form of )
(where is the number of prime factors of the form of )
The last two formulas are special cases of
which generate infinitely many analogous formulas for when
Some formulas relating and harmonic numbers are given here. Further infinite series involving π are:
where is the Pochhammer symbol for the rising factorial. See also Ramanujan–Sato series.
Machin-like formulae
(the original Machin's formula)
Infinite products
(Euler) where the numerators are the odd primes; each denominator is the multiple of four nearest to the numerator.
(see also Wallis product)
(another form of Wallis product)
Viète's formula:
A double infinite product formula involving the Thue–Morse sequence:
where and is the Thue–Morse sequence .
Arctangent formulas
where such that .
where is the k-th Fibonacci number.