Free online calculators with step-by-step solutions
Every calculator shows its work: the formula, the solution steps for your own numbers, and worked examples you can follow by hand.
School & math
- GCF CalculatorFind the greatest common factor of two or more numbers with full Euclidean-algorithm steps, plus the LCM for a pair. Free, instant, no ads in results.
- GPA CalculatorCalculate your GPA on the 4.0 scale: add courses with letter grades and credits, see quality points and the math behind your grade point average.
- Percentage CalculatorThree percentage tools with steps: find X% of a number, what percent X is of Y, and the percentage increase or decrease between two values.
- Fraction CalculatorAdd, subtract, multiply and divide fractions with full steps: common denominators, reciprocals, reducing to lowest terms, and mixed-number answers.
- Cumulative GPA CalculatorCombine your current GPA and completed credits with this semester's grades to get your new cumulative GPA — with the quality-point math shown.
- Final Exam CalculatorFind the score you need on the final exam to hit your target course grade, from your current grade and the final's weight — with the math shown.
- Percentage Increase CalculatorCalculate the percentage increase or decrease between two values, or apply a percent increase to a number — with the division steps shown.
- Percentage Difference CalculatorFind the percentage difference between two values — the symmetric comparison that divides by their average, with steps and when to use it instead of % change.
- LCM CalculatorFind the least common multiple of two or more numbers via the GCF method, with steps shown — plus when you need the LCM for fractions and schedules.
- Decimal to Fraction CalculatorConvert a decimal to a fraction in lowest terms with place-value steps: write it over a power of ten, reduce by the GCF, get the mixed-number form.
- Volume CalculatorCalculate the volume of a box, cylinder, sphere or cone in inches, feet, cm or meters — with liters and US gallons conversion and the formula steps.
- Area CalculatorCalculate the area of a rectangle, triangle, circle or trapezoid with the formula steps shown — the geometry companion to our square footage calculator.
- College GPA CalculatorCalculate college GPA from letter grades and credit hours on the 4.0 scale — quality points shown step by step, with semester and repeat-policy guidance.
- High School GPA CalculatorCalculate high school GPA both ways at once: unweighted on the 4.0 scale and weighted with honors +0.5 and AP/IB +1.0 — with the math shown.
- Mixed Number CalculatorAdd, subtract, multiply and divide mixed numbers with steps: convert to improper fractions, compute, reduce, and convert back to a mixed number.
- Ratio CalculatorSimplify ratios to lowest terms (decimals welcome) and solve proportions A:B = C:x by cross-multiplication — with every step shown.
- Slope CalculatorFind the slope from two points — rise over run — plus the line's equation y = mx + b, the distance between the points and the angle, with steps.
- Quadratic Formula CalculatorSolve ax² + bx + c = 0 with the quadratic formula: discriminant, both roots (real or complex) and the vertex — every step shown.
- Square Root CalculatorSquare roots with the simplified radical form (√72 = 6√2), perfect-square detection and decimal value — factorization steps included.
- Scientific Notation ConverterConvert numbers to scientific notation and back — decimal-point moves counted step by step, with E-notation for calculators and code.
- Pythagorean CalculatorSolve a² + b² = c² for the hypotenuse or a missing leg of a right triangle, with the squaring and square-root steps shown.
- Percent of a NumberFind a percentage of any number with the two-step method shown — convert the percent to a decimal, multiply — plus quick preset buttons and mental shortcuts.
- Triangle CalculatorSolve any triangle from three sides (SSS) or two sides and the included angle (SAS): all sides, angles, area and perimeter with law-of-cosines steps.
Dates & time
- Date CalculatorCount the days between two dates (with weeks and a years/months/days breakdown) or add and subtract days from a date — with the counting logic shown.
- Age CalculatorFind exact age from a date of birth: years, months and days, total days lived, and the date of the next birthday — with the calendar math shown.
- Hours CalculatorCount hours and minutes between two times, subtract unpaid breaks, and convert to decimal hours for payroll. Handles overnight shifts automatically.
- Time Card CalculatorFree weekly time card calculator: enter daily start, end and breaks to total the week's hours in decimal form, with optional gross pay at an hourly rate.
- Time to Decimal ConverterConvert hours and minutes to decimal hours for payroll, and decimal hours back to time — with the ÷60 math shown and a minutes cheat sheet.
- Chronological Age CalculatorCalculate chronological age in years, months and days between birth date and test date — the exact calendar method used in assessments and pediatrics.
- Duration CalculatorCalculate the exact duration between two dates and times — days, hours and minutes, plus decimal totals — with the counting steps shown.
- Time CalculatorAdd and subtract times in hours, minutes and seconds with a running total — carries at 60 handled for you, with the seconds math shown.
Home & construction
- Concrete CalculatorWork out how much concrete you need for a slab: cubic yards, 60 lb and 80 lb bag counts, and waste allowance — with the math shown step by step.
- Square Footage CalculatorCalculate square footage from length and width, convert to square yards, meters and acres, and estimate material cost from a price per square foot.
- Sq Ft ↔ Acres ConverterConvert square feet to acres and acres to square feet (1 acre = 43,560 sq ft), with the division shown and real-world size comparisons.
- Concrete Slab CalculatorConcrete for a slab: cubic yards with waste allowance and material cost at your local ready-mix price — multiple slabs supported, steps shown.
- Cubic Feet CalculatorCalculate cubic feet from length, width and height — each in inches or feet — with cubic yards and cubic inches, and the conversion steps shown.
- QUIKRETE Bag CalculatorHow many QUIKRETE bags for your pour: enter the slab size and bag weight (40–90 lb) to get the bag count from the manufacturer's published yields.
- Paint CalculatorWork out how many gallons of paint a room needs: walls from the dimensions, minus doors and windows, times coats, at the real spread rate — steps shown.
Health & fitness
Random generators
- Random Word GeneratorGenerate random English words — nouns, verbs, adjectives or a mix — for games, brainstorming, writing prompts and vocabulary practice. One-click copy.
- Random Letter GeneratorGenerate random letters from A to Z — uppercase or lowercase, one at a time or a whole set, with an optional no-repeats mode. Free and instant.
- Random Animal GeneratorGenerate random animals from a curated list of 200+ species — filter by mammals, birds, reptiles, sea creatures or insects. For games, art and prompts.
- Fake Name GeneratorGenerate random realistic US names for test data, placeholders, writing and mockups — female, male or mixed pools, with one-click copy. Runs locally.
- Random Number 1–3Generate a random number between 1 and 3 with a fair, cryptographic pick — each value has an equal 1-in-3 chance. Presets for other ranges included.
- Random Number 1–4Generate a random number between 1 and 4 with a fair, cryptographic pick — each value has an equal 1-in-4 chance. Presets for other ranges included.
- Random Number 1–5Generate a random number between 1 and 5 with a fair, cryptographic pick — each value has an equal 1-in-5 chance. Presets for other ranges included.
- Random Number 1–6Generate a random number between 1 and 6 with a fair, cryptographic pick — each value has an equal 1-in-6 chance. Presets for other ranges included.
- Random Number 1–10Generate a random number between 1 and 10 with a fair, cryptographic pick — each value has an equal 1-in-10 chance. Presets for other ranges included.
- Random Number 1–100Generate a random number between 1 and 100 with a fair, cryptographic pick — each value has an equal 1-in-100 chance. Presets for other ranges included.
- Surname GeneratorGenerate random last names from the most common US surnames — for characters, placeholder data and pen names. Batch generation with one-click copy.
- Random Color GeneratorGenerate random colors as live swatches — curated named colors or any hex value — with hex codes ready to copy for design, art and CSS.
- Random Team GeneratorPaste a list of names and split it into fair random teams — even sizes, shuffle-and-deal method, copyable results. For class, sports and trivia nights.
- Random Country GeneratorPick random countries from all 195 — for geography quizzes, travel roulette, writing prompts and games. Repeat-free batches, one-click copy.
- DnD Name GeneratorGenerate D&D character names by race — human, elf, dwarf, half-orc, halfling — built from race-flavored syllables with matching surnames.
- Username GeneratorGenerate available-sounding usernames in three styles — CamelCase, snake_case and short — from adjective-noun-number patterns. Private, runs in-browser.
Converters
- Unit ConverterConvert length, weight, volume and temperature between US and metric units with exact factors and steps — feet to meters, lb to kg, °F to °C.
- Kg → Lbs ConverterConvert kilograms to pounds instantly (1 kg = 2.20462 lbs) with the exact math shown and a table of common weights from 40 to 120 kg.
- Lbs → Kg ConverterConvert pounds to kilograms instantly (1 lb = 0.45359237 kg exactly) with the math shown and a table of common weights from 100 to 280 lbs.
Everyday life
- Tip CalculatorFree tip calculator: enter the bill and tip percent to get the tip, total, and per-person split — with the math shown step by step.
- Height CalculatorPredict a child's adult height from the parents' heights with the mid-parental (Tanner) method — result in feet/inches and cm, with the math and range shown.
Pets
- Dog Age CalculatorConvert dog years to human years with the veterinary size chart and the UCSD epigenetic formula — not the old times-7 myth. Steps included.
- Dog Name GeneratorGenerate dog name ideas from 200+ popular girl and boy dog names — shuffle until one fits, then copy your shortlist. Tips for picking a trainable name.
- Cat Name GeneratorGenerate cat name ideas from popular girl, boy and black-cat name lists — shuffle, shortlist and copy. With tips on names cats respond to.
- Puppy Weight CalculatorEstimate your puppy's adult weight from its current weight, age and expected size class, using the published milestone rules — with the math and caveats shown.
- Dog Food CalculatorHow much to feed your dog: daily calories from the veterinary RER formula and life-stage factors, converted to cups of your actual food — steps shown.