Math
1,470 math calculators: percentages, fractions, equations, geometry, trigonometry, statistics and number theory. Each one shows the method in plain words, so you get the answer and understand how it was reached, free in your browser.
Centroid calculator
Find the middle of a set of points by averaging their coordinates: (0, 0), (4, 0) and (0, 3) have their centroid at (1.3333333333, 1).
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Centroid of a triangle
Find a triangle's balance point from its three corners: vertices (0, 0), (6, 0) and (0, 9) give a centroid at (2, 3), the plain average of their x and y values.
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Change of base calculator
Get a logarithm in any base, not just ln or log10: log base 10 of 1000 is 3, worked out as ln 1000 divided by ln 10.
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Characteristic polynomial calculator
Get the characteristic polynomial of any square matrix up to 12×12: the matrix with rows 2, 1 and 1, 2 gives λ² − 4λ + 3, with its trace of 4 and determinant of…
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Check similarity in right triangles
Find out whether two right triangles have the same shape: legs of 3 and 4 against legs of 6 and 8 are similar, with a scale factor of 2.
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Chinese remainder calculator
Solve simultaneous congruences in one step: x ≡ 2 (mod 3), x ≡ 3 (mod 5) and x ≡ 2 (mod 7) have 23 as their smallest non-negative solution, and the answer…
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Cholesky decomposition calculator
Split a symmetric positive definite matrix into a lower triangle L times its transpose: the classic 3×3 example whose first row is 4, 12, −16 gives an L with 2…
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Circle center from three points
Recover the circle behind three measured points: (0, 0), (4, 0) and (0, 3) give a center at (2, 1.5), a radius of 2.5 and the equation (x − 2)² + (y − 1.5)² =…
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Circle diameter calculator
Get a circle's diameter from whichever measurement you have: a radius of 5 gives 10, and a tape wrapped around the edge that reads 31.4159 also gives 10 across.
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Circle length calculator
Work out the length around a circle from whichever measurement you have, the radius or the diameter, where a radius of 5 gives 31.415927.
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Circle formula
Both circle equations from a center and a radius: center (3, −2) and radius 5 give (x − 3)² + (y + 2)² = 25 and x² + y² − 6x + 4y − 12 = 0.
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Circle measurements
One radius, three answers: a circle with a radius of 5 has a diameter of 10, a circumference of 31.415927 and an area of 78.539816.
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Seeded random number generator in a range
With a range from 10 to 100 and the seed 2026, the result is 11, and it will be 11 again whenever you repeat those inputs.
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Seeded random string generator
Type a seed such as release-2026-08, ask for 24 characters, and you get DRWAF7foOYXgYWU4VpEGTuft every time you repeat those settings, so sample codes and demo…
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Circle perimeter calculator
Find the length of a circle's edge from its radius alone, so a radius of 5 gives a perimeter of 31.415927, in the same unit you measured in.
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Circle theorems calculator
Enter one angle, pick a circle theorem and get the related angle, so a central angle of 80 degrees gives an inscribed angle of 40 on the same arc.
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Circumcenter of a triangle
Find the point that sits at the same distance from a triangle's three corners: for vertices (0, 0), (4, 0) and (0, 3) the circumcenter is (2, 1.5), the midpoint…
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Circumference calculator
Measure across a circle and get the length around it: a diameter of 10 gives a circumference of 31.415927, in the same unit you measured in.
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Circumference to diameter
Wrap a tape around something round and turn that reading into its width: a circumference of 31.41592653589793 gives a diameter of 10.
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Circumference and area of a circle
One radius gives you both numbers a round object needs: a radius of 5 has a circumference of 31.415927 and an area of 78.539816.
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Circumference to Radius Calculator
Measure the edge and get the radius a drawing or a machine asks for: a circumference of 31.415927 gives a radius of 5, in the same unit.
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Circumscribed circle
Find the one circle that runs through three points: for (0, 0), (4, 0) and (0, 3) the circumscribed circle is centered at (2, 1.5) with a radius of 2.5, the…
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Classifying triangles by sides and angles
Enter three side lengths and get both labels at once: 3, 4 and 5 make a scalene right triangle. It sorts by sides and by angles, and first checks that the…
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Clock angle calculator
At 3:30 the hands of a clock are 75 degrees apart, not 90, because the hour hand keeps creeping toward four.
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Cofactor expansion calculator
Expand a determinant along the row or column you pick and see every term: in the 3×3 example, the first row contributes 4, 5 and −60, which add up to −51.
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Cofactor matrix calculator
Get every signed cofactor of a square matrix at once: for rows (1, 2) and (3, 4), the cofactor matrix has rows (4, −3) and (−2, 1), with each checkerboard sign…
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Cofunction calculator
Evaluate any trig function through its partner at the complementary angle, so sin(30) becomes cos(60), which is 0.5, and you see the cofunction and the…
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Coin rotation paradox
Find how many turns a circle makes rolling around another: two identical coins give 2 rotations, not 1, because the count is (R + r) / r.
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Column space calculator
Get a column space basis straight from the pivot columns. For rows (1, 2, 3), (2, 4, 6) and (1, 0, 1), the original columns (1, 2, 1) and (2, 4, 0) form the…
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Least common denominator calculator
Get the smallest denominator two fractions can share: for 12 and 18 it is 36, so 5/12 and 7/18 become 15/36 and 14/36 and add in one step.
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Common factor calculator
See every whole number that divides all your integers exactly: 12, 18 and 30 share the factors 1, 2, 3 and 6, and their greatest common divisor is 6.
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Least common multiple calculator
Get the smallest positive number that two integers both divide: the least common multiple of 12 and 18 is 36, so machines cycling every 12 and every 18 minutes…
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Lucas number calculator: L_n from L0=2, L1=1, free bigint
Get any term of the Lucas sequence exactly: it starts 2, 1, 3, 4, 7, 11, and the 10th term is 123.
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Palindrome number checker
Check whether a number reads the same forwards and backwards in any base from 2 to 36: 121 is a palindrome in base 10, and 5 is one in base 2, written…
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Basic proportionality (Thales)
With AD of 3, DB of 6, AE of 2 and EC of 4, both ratios are 0.5, so Thales' proportion holds. Enter the four segments cut by a parallel line and check the…
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Isosceles trapezoid calculator
Enter the two bases and the height of an isosceles trapezoid and get the whole figure: bases of 10 and 6 with a height of 4 give an area of 32, legs of…
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German number to words
Type 21 and get einundzwanzig: the converter writes whole numbers from 0 to 999999 as German words, with the unit before the ten and hundert and tausend joined…
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Italian number to words
21 becomes ventuno, not ventiuno: the converter spells whole numbers from 0 to 999999 in Italian, dropping the vowels Italian drops and choosing mille or mila…
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Portuguese number to words
21 is written vinte e um: the converter spells whole numbers from 0 to 999999 in Portuguese, placing the linking e where it belongs and choosing correctly…
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Oblique cone volume calculator
A cone with radius 3 and perpendicular height 5 holds about 47.12389 cubic units, tilted or not. Enter the base radius and the height to get the volume and the…
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German ordinal words
1 becomes erste and 2 becomes zweite: the converter gives the German ordinal word for any whole number from 1 to 100, with the special forms of the first twenty…
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Prolate spheroid calculator
Enter the two semi-axes of a prolate spheroid and get its volume, surface area and eccentricity: with a of 5 and c of 3, the volume is 188.495559, the surface…
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Ptolemy theorem calculator
Solve a missing side or diagonal of a quadrilateral inscribed in a circle with Ptolemy's theorem: with sides 3, 4, 5 and 6 and one diagonal of 5, the other…
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Spherical law of cosines
Find side c of a spherical triangle from sides a and b and the angle C between them, or recover C from all three sides: sides of 1 and 1 with an angle of 1…
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French words to number
Type a French number in words and get it in digits: “vingt et un” becomes 21. It reads whole numbers from zéro up to 999, with or without hyphens.
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Fréchet distribution calculator
Enter a point and the three numbers of a Fréchet distribution: at the point 1, with shape 2, scale 1 and location 0, the cumulative probability is 0.367879 and…
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3D distance calculator
From (1.5, 2.5, 3.5) to (4.5, 6.5, 8.5) the gaps are 3, 4 and 5, so the straight-line distance is 7.07106781187.
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Compare cost per serving for two recipes
Find which of two recipes is cheaper per serving, even when batch sizes differ: a batch costing 24 for 8 servings comes to 3 each, while one costing 18 for 4…
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Split a tip pool by hours worked
A pool of 100 split across shifts of 8, 6 and 4 hours pays 44.45, 33.33 and 22.22, and the amounts add back to the full pool to the cent.
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Compare unit price between products
A 12-item pack at 4.50 costs 0.375 per item, while a 20-item pack at 6.40 costs 0.32, so the bigger pack is the better value.
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Group expense settle-up
Enter each person's net balance and get a short list of who pays whom: if Alice is owed 50 while Bob owes 30 and Carol owes 20, two payments to Alice clear the…
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Simplify mixed fraction
Reduce a mixed number or fraction to lowest terms and get both forms at once: 2 4/6 becomes 2 2/3, which is 8/3 as an improper fraction.
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Add or subtract days from a date
28 December 2024 plus 5 days is 2 January 2025. Enter a date and a number of days, positive to go forward or negative to go back, and get the exact calendar…
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Calculate countdown to a target date in days, hours and minutes
Find how long remains until a date: from 25 July 2026, 10:15 UTC, to 28 July 2026, 12:45 UTC, is 3 days, 2 hours and 30 minutes, or 4470 minutes.
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Calculate basal metabolic rate with the Mifflin-St Jeor equation
A 35-year-old woman weighing 70 kg and 175 cm tall uses about 1457.75 kcal a day at rest, according to the Mifflin-St Jeor equation.
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Calculate paint needed for an area
120 m² of wall at 10 m² per liter needs 12 liters for one coat and 24 liters for two. Enter the area, the coverage rate on the can and the number of coats to…
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Estimate pregnancy due date
Enter the first day of the last period and today's date to get the estimated due date: a period that began on 1 January 2026 points to 8 October 2026, and by 15…
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Predict race finish time with Riegel's formula
Predict a finish time for a new race distance from a recent result: a 10 km run in 40 minutes points to a half marathon in 1:28:15, using Riegel's formula with…
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Calculate time difference between UTC offsets
UTC−5 and UTC+5:30 are 10.5 hours apart, with the second one ahead. Enter two fixed offsets from UTC−12 to UTC+14 and get the gap in hours, the signed…
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Calculate tiles needed for a floor area with waste allowance
A 24 m² room laid with 0.6 × 0.4 m tiles and 10% extra for cuts needs 110 tiles. Enter the floor area, the size of one tile and your waste allowance, and get…
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