Circle Calculator (radius / diameter / circumference / area)

Percent of, percent change, and percent add/subtract in one.

Enter 2–6 positive integers to get the greatest common divisor (HCF / GCD) and least common multiple (LCM), with the Euclidean step chain shown.

Enter a list of numbers to get the mean, median, mode, range plus standard deviation, variance and total.

Enter the coefficients of ax² + bx + c = 0 to find the real or complex roots, discriminant and vertex.

Estimate a password's bit entropy, brute-force time and strength tier. All computation happens in your browser.

Convert between standard decimal numbers and scientific notation, with significant figures and order of magnitude.

Compute permutations P(n,r), combinations C(n,r) and factorial n! — useful for probability problems, lottery odds and combinatorics homework.

Paste a list of numbers to compute mean, median, sample and population variance and standard deviation — with the working shown.

Solve a triangle from 3 sides, 2 sides + 1 angle, or 2 angles + 1 side — area, perimeter and remaining parts via the law of sines / cosines.

Given any two sides of a right triangle (two legs, or one leg plus the hypotenuse), instantly find the third side, area, perimeter and the two non-right angles.

Two-way conversion between Arabic numbers (1–3999) and Roman numerals (I, V, X, L, C, D, M) — handy for typesetting, chapter titles and homework.

Enter two points (x₁, y₁) and (x₂, y₂) to instantly get the slope, y-intercept, line equation y = mx + b, distance, and midpoint — a classroom staple for algebra and coordinate geometry.

Enter group size n to see the probability that at least two people share a birthday — the classic birthday problem.

Compute logₐ(x) for any base — natural log (ln), common log (log₁₀), binary log (log₂) and a custom base, with the change-of-base steps shown.

Enter a value, the mean and the standard deviation to compute the z-score and the corresponding normal-distribution percentile and probabilities.

Enter the screen resolution and diagonal size to get pixel density (PPI), real width/height, dot pitch and total pixel count.

Enter the number of tickets / selections and see the actual probability of hitting first, second … prizes in a Mark Six (6-of-49) draw.

Convert any decimal (including repeating decimals) to a simplified fraction and a mixed number.

Give a sphere any one of radius, diameter, surface area or volume and instantly get the other three — plus the great-circle circumference and area.

Enter the radius and height of a cylinder to get volume (π r²h), lateral surface, base area and total surface area.

Factor any integer from 2 up to 10¹² into primes, see the canonical exponent form, count and list all divisors.

Compute the n-th root of the product of n positive numbers — the right average for growth rates, returns and ratios — alongside the arithmetic mean for comparison.

Enter any integer n from 0 to 1500 to instantly compute F(n) and F(n−1) with BigInt precision, the consecutive-term ratio (converging to the golden ratio φ) and the first 30 terms of the sequence.