My Calculator Stack
481 free calculators. No sign-up.
No login and no account — just open a tool. What is 15% of a bill? What BMI follows from weight and height? What does a loan payment look like? Convert acres, hectares, and other units — then read the formula beside the form.
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Popular calculators
Age Calculator
Calculate age in years, months, and days from a birth date.
Open tool →Average Calculator
Compute the arithmetic mean of a list of numbers.
Open tool →BMI Calculator
Body mass index from weight and height (Metric or US units).
Open tool →Free Fall Calculator
Distance and impact speed for free fall from rest: s = ½ g t², v = g t.
Open tool →Future Value Calculator
Project how a present amount grows at a periodic rate.
Open tool →Percentage Calculator
Find a percent of a number, reverse percentages, and percent change.
Open tool →Scientific Calculator
Keyboard-first scientific calculator with DEG/RAD trig, 2nd functions, memory, history, and display modes.
Open tool →Tip Calculator
Calculate tip amount and total bill from a tip percentage.
Open tool →Unit Converter
Convert length, mass, temperature, area, volume, energy, and more.
Open tool →Browse by category
Indexable hubs with crawlable links to every tool in the family.
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Learn the math
Short tutorials that unpack the formulas behind each tool.
How to Calculate BMI
Body mass index (BMI) is a screening ratio: body mass divided by the square of height. This tutorial walks through the SI formula, a 70 kg / 1.75 m worked example, and WHO adult category bands you can try with sliders. BMI is not a diagnosis of health, body fat, or disease.
Read tutorial → Fitness · 5 minHow to Calculate BMR
Basal metabolic rate (BMR) estimates the calories your body uses at rest. This tutorial walks through the Mifflin–St Jeor formulas, a 70 kg / 175 cm / age 30 worked example, and a playground that substitutes your numbers. BMR is an estimate of resting energy, not a meal plan or a medical assessment.
Read tutorial → Physics · 8 minHow to Calculate Angular Resolution with the Rayleigh Criterion
Two point sources are just resolved when the first dark ring of one Airy pattern sits on the peak of the other. For a circular aperture that split is θ = 1.22 λ / D. This tutorial works 550 nm through a 10 cm opening to 6.71×10⁻⁶ rad ≈ 1.38″, the same defaults as the Angular Resolution Calculator.
Read tutorial → Geometry · 7 minHow to Find the Centroid of a Right Triangle at (b/3, h/3)
If a right triangle has its right angle at the origin, the centroid is not a mystery point you have to construct from scratch. From that right-angle vertex, G = (b/3, h/3): one-third of the way along the base and one-third of the way up the height. This tutorial derives that shortcut from the three-vertex average, works b = 6 and h = 4, and opens the same points in the Centroid of a Triangle Calculator.
Read tutorial → Personal Finance · 5 minHow to Calculate Compound Interest
Compound interest reinvests earned interest into the balance, so later periods earn interest on interest. This tutorial walks through A = P(1 + r/m)^{mt}, a $5,000 / 4% / 10-year monthly worked example, and a playground that compares compound growth with simple interest. Figures are illustrative; fees and taxes are omitted.
Read tutorial → Math · 10 minHow to Calculate Your GPA for Free Online
You can calculate a college GPA for free on this site without creating an account or uploading a transcript. This walkthrough is for university credit hours on a 4.0 scale: gather what your registrar actually uses, run one term in the Semester GPA Calculator, convert assignment percents when you still have scores instead of letters, check whether a course goal is still reachable on the final, and plan a cumulative target. The pages are teaching checks, not an official record.
Read tutorial → Math · 5 minHow to Calculate a Percentage
A percentage compares a part to a whole on a scale of 100. This tutorial walks through the three problems the Percentage Calculator solves: what is P% of X, X as a percent of Y, and percent change from A to B. The worked example uses the same 15% of 80 defaults as the calculator.
Read tutorial → Geometry · 8 minHow to Calculate Surface Area to Volume Ratio
Surface-to-volume ratio is the outside divided by the inside: S/V. This tutorial uses the three solids the Surface Area to Volume Ratio Calculator actually takes — sphere, cube, and rectangular box — works the default sphere of radius 3 to S/V = 1, and lets you switch shapes in a playground.
Read tutorial →Formula sheets
One printable sheet per category.
Math formulas
One printable sheet for 139 Math tools — formulas collected from each calculator’s How it works.
Open sheet → FitnessFitness formulas
One printable sheet for 14 Fitness tools — formulas collected from each calculator’s How it works.
Open sheet → Personal FinancePersonal Finance formulas
One printable sheet for 14 Personal Finance tools — formulas collected from each calculator’s How it works.
Open sheet →