Most popular
The tools every student starts with
Final Grade Calculator
What you need on your final exam.
Word Counter
Words, characters, reading time — live as you type.
GPA Calculator
Standard 4.0 scale, weighted or unweighted.
Pomodoro Timer
Focus timer with a visual ring and breaks.
Mean, Median, Mode
Mean, median, mode, range, and quartiles from a data set.
Compound Interest
Growth with compounding, A = P(1 + r/n)^(nt).
Citation Generator
APA, MLA, and Chicago citations in seconds.
Periodic Table
Interactive, filterable, element details.
BMI Calculator
Body mass index from height and weight.
Time Zone Converter
Convert a time between any two time zones.
Recently added
The newest calculators and references on Knidox
Distance Modulus Calculator
Solve for distance, apparent, or absolute magnitude from the distance modulus.
Telescope Magnification Calculator
Magnification, focal ratio, and exit pupil from your telescope and eyepiece.
Hubble’s Law Calculator
Relate a galaxy’s recession velocity and distance with v = H₀d.
Wien’s Law Calculator
Convert between a blackbody’s temperature and its peak wavelength.
Moon Phase Calculator
Find the Moon phase and illumination for any date.
Planet Weight Calculator
See what you would weigh on every planet, the Moon, and the Sun.
Protein Intake Calculator
Find your daily protein target in grams by body weight and goal.
Lean Body Mass Calculator
Estimate lean body mass with the Boer and James formulas.
VO₂ Max Estimator
Estimate VO₂ max from a Cooper run test or your resting heart rate.
Waist-to-Hip Ratio Calculator
Work out your waist-to-hip ratio and WHO health-risk category.
Body Surface Area Calculator
Calculate BSA from height and weight with the Mosteller and Du Bois formulas.
One-Rep Max Calculator
Estimate your 1RM from reps and weight with the Epley and Brzycki formulas.
Grades
Figure out where you stand
Final Grade Calculator
What you need on your final exam.
GPA Calculator
Standard 4.0 scale, weighted or unweighted.
GPA Goal Planner
The GPA you need in remaining credits to hit a target cumulative GPA.
Grade Curve Calculator
Curve a raw score with flat, linear-scale, or square-root methods.
Rubric Grade Calculator
Score a project from rubric criteria — overall % and letter grade.
GPA Retake Calculator
Recalculate your GPA after retaking a course — replacement or averaging.
Weighted GPA
AP / IB / Honors with bonus points.
See all 12 Grades toolsWriting
Essays, papers, and citations
Word Counter
Words, characters, reading time — live as you type.
Citation Generator
APA, MLA, and Chicago citations in seconds.
Essay Outline Builder
Turn a thesis and key points into a structured essay outline.
Character Counter
With/without spaces. Tweet & SMS limits.
Reading Time
Estimate reading time at 250 WPM.
Words to Pages
By font, size, and line spacing.
Readability Score
Flesch-Kincaid, Gunning Fog, SMOG.
See all 18 Writing toolsConvert
GPAs, grading systems, and test scores — for international students
GPA Scale Converter
Convert a GPA between US, UK, German, Indian, and percentage scales.
IELTS Band Score Calculator
Overall IELTS band from your four section scores, with correct rounding.
ACT Composite Score Calculator
ACT composite score from your English, Math, Reading, and Science scores.
SAT Superscore Calculator
Your best SAT superscore from the top section scores across sittings.
German Grade Converter
Convert a foreign grade to the German 1–5 scale with the Bavarian formula.
Indian CGPA to Percentage
Convert between CGPA and percentage using the CBSE and 10-point scales.
TOEFL Score Calculator
TOEFL iBT total from your four section scores, with a CEFR level.
See all 26 Convert toolsStudy
Timers, planners, and focus tools
Pomodoro Timer
Focus timer with a visual ring and breaks.
Typing Speed Test
WPM and accuracy, live feedback.
Spaced Repetition Scheduler
Next review interval for a flashcard using the SM-2 algorithm.
Forgetting Curve Calculator
Estimated memory retention over time from the forgetting curve.
Study Hours Planner
Weekly and semester study hours from your credit load.
Focus & Break Planner
Fit focus and break cycles into your time with proven work rhythms.
Attendance Calculator
How many classes you can miss and stay above the required attendance %.
See all 15 Study toolsMath
Calculus, algebra, trig, and probability
Percentage Calculator
Percent of, increase, decrease, change.
Quadratic Solver
ax² + bx + c = 0, step by step.
System of Equations
2×2 and 3×3 linear systems.
Long Division Calculator
Divide two numbers with the full long-division working shown.
Synthetic Division Calculator
Divide a polynomial by (x − c) with the synthetic-division steps.
Completing the Square
Rewrite a quadratic as a(x − h)² + k, step by step.
Partial Fractions Calculator
Decompose a rational function into partial fractions with steps.
See all 34 Math toolsGeometry
Shapes, area, volume, and angles
Distance & Midpoint
Distance and midpoint between two points.
Pythagorean Theorem
Solve a² + b² = c² for any missing side.
Area & Volume
Area and volume of common 2D and 3D shapes.
Triangle Solver
Solve a triangle from sides and angles (SSS, SAS, ASA, AAS).
Circle Calculator
Radius, diameter, circumference, and area of a circle.
Sphere Calculator
Volume and surface area of a sphere from its radius.
Cylinder Calculator
Volume and surface area of a cylinder from radius and height.
See all 10 Geometry toolsChemistry
pH, molarity, equations, periodic table
Periodic Table
Interactive, filterable, element details.
pH Calculator
From H⁺ concentration or Ka.
Stoichiometry Calculator
Mole ratios and masses from a reaction.
Molar Mass
Enter a formula → molecular weight.
Equation Balancer
Auto-balance chemical equations.
Dilution Calculator
Solve C₁V₁ = C₂V₂ for any variable.
Ideal Gas Law
PV = nRT, solve for any variable.
See all 26 Chemistry toolsPhysics
Motion, forces, circuits, and waves
Force Calculator
F = ma, solve for any variable.
Kinematics Solver
SUVAT equations of motion.
Projectile Motion
Range, height, and flight time.
Density Calculator
ρ = m / V, solve for any variable.
Wave Speed Calculator
v = fλ, speed, frequency, wavelength.
Pendulum Period
T = 2π√(L/g), period or length.
Specific Heat
Q = mcΔT, solve for any variable.
See all 29 Physics toolsAstronomy
Redshift, parallax, and light-years
Planet Weight Calculator
See what you would weigh on every planet, the Moon, and the Sun.
Moon Phase Calculator
Find the Moon phase and illumination for any date.
Wien’s Law Calculator
Convert between a blackbody’s temperature and its peak wavelength.
Hubble’s Law Calculator
Relate a galaxy’s recession velocity and distance with v = H₀d.
Telescope Magnification Calculator
Magnification, focal ratio, and exit pupil from your telescope and eyepiece.
Distance Modulus Calculator
Solve for distance, apparent, or absolute magnitude from the distance modulus.
Redshift to Velocity Calculator
Recession velocity from redshift z, low-z and relativistic.
See all 12 Astronomy toolsElectronics
Ohm’s law, dividers, capacitors, and more
Ohm’s Law
Voltage, current, resistance, power.
Resistors (Series & Parallel)
Total resistance of resistors in series or parallel.
Resistor Color Code
Resistance and tolerance from the color bands.
Voltage Divider Calculator
Output voltage from two resistors in a divider.
LED Resistor Calculator
Series resistor value for an LED from supply and forward voltage.
Capacitor Energy Calculator
Energy and charge stored in a capacitor from capacitance and voltage.
RC Time Constant Calculator
Time constant τ = RC and the charge/discharge curve.
See all 10 Electronics toolsEngineering
Beams, stress, torque, and gears
Beam Deflection Calculator
Maximum deflection of a beam under a central or end point load.
Stress and Strain Calculator
Axial stress, strain, and elongation from force and dimensions.
Young’s Modulus Calculator
Elastic modulus from stress and strain, or axial deformation.
Torque to Power Calculator
Convert between torque, rotational speed (RPM), and power.
Gear Ratio Calculator
Gear ratio with output speed and torque from tooth counts.
Factor of Safety Calculator
Factor of safety from material strength and applied stress.
Biology
Genetics, populations, and cells
Punnett Square
Mono- and dihybrid crosses, visualized.
DNA Codon Translator
Translate DNA/RNA into amino acids.
Hardy-Weinberg
Allele & genotype frequencies.
Allele Frequency
p and q from genotype counts.
Serial Dilution
Concentration at every tube.
Dihybrid Cross
Two-trait Punnett square and 9:3:3:1 ratio.
Surface-Area-to-Volume
SA:V ratio for cells and shapes.
See all 15 Biology toolsHealth & Fitness
Body, calories, and fitness
BMI Calculator
Body mass index from height and weight.
One-Rep Max Calculator
Estimate your 1RM from reps and weight with the Epley and Brzycki formulas.
Body Surface Area Calculator
Calculate BSA from height and weight with the Mosteller and Du Bois formulas.
Waist-to-Hip Ratio Calculator
Work out your waist-to-hip ratio and WHO health-risk category.
VO₂ Max Estimator
Estimate VO₂ max from a Cooper run test or your resting heart rate.
Lean Body Mass Calculator
Estimate lean body mass with the Boer and James formulas.
Protein Intake Calculator
Find your daily protein target in grams by body weight and goal.
See all 19 Health & Fitness toolsStatistics
Distributions, tests, and intervals
Z-Score Calculator
Standardize a value and find its percentile.
Mean, Median, Mode
Mean, median, mode, range, and quartiles from a data set.
Standard Deviation
Mean, variance, and SD for any dataset.
P-Value Calculator
From a test statistic and distribution.
Confidence Interval
For a mean or proportion.
Normal Distribution
Probabilities under the bell curve.
T-Test Calculator
One- and two-sample tests with p-value.
See all 21 Statistics toolsFinance
Interest, loans, and budgeting
Compound Interest
Growth with compounding, A = P(1 + r/n)^(nt).
Simple Interest
Interest = principal × rate × time.
Loan & EMI Calculator
Monthly payment, total interest, and schedule.
Discount Calculator
Sale price and amount saved from a percent off.
Tip Calculator
Tip amount and total, split across people.
Savings Goal
Monthly saving needed to reach a target.
ROI Calculator
Return on investment, gain, and annualized return.
See all 26 Finance toolsEconomics
Elasticity, GDP, and surplus
Price Elasticity of Demand
Elasticity of demand from price and quantity, midpoint method.
Real GDP Calculator
Real GDP, nominal GDP, and the GDP deflator from any two.
CPI Inflation Rate Calculator
Inflation rate between two Consumer Price Index values.
Consumer & Producer Surplus
Consumer, producer, and total surplus from a linear market.
Comparative Advantage Calculator
Opportunity cost and comparative advantage for two producers.
Spending Multiplier Calculator
The multiplier and change in GDP from the marginal propensity to consume.
Computer Science
Logic, numbers, and bits
Big-O Complexity Reference
Common time complexities with examples and a growth comparison.
Hamming Distance Calculator
Count the differing positions between two equal-length strings.
Hexadecimal Calculator
Add, subtract, multiply, and divide hexadecimal numbers.
IEEE 754 Float Converter
The sign, exponent, and mantissa bits of a 32-bit float.
Set Operations Calculator
Union, intersection, and difference of two sets.
Gray Code Converter
Convert between binary and reflected Gray code.
Truth Table Generator
Truth table for any boolean expression.
See all 23 Computer Science toolsLanguage
Conjugation and declension helpers
Spanish Verb Conjugator
Conjugate Spanish verbs, 5 tenses.
French Numbers in Words
Write any number in French, with the 70/80/90 forms handled.
Spanish Numbers in Words
Write any number in Spanish, with gender and apocope handled.
German Numbers in Words
Write any number in German, as one compound word.
German Cases & Articles
Der/die/das and ein declension across all four German cases.
False Friends Reference
Words that look alike across languages but mean something else.
IPA Pronunciation Reference
IPA vowels and consonants with example words and descriptions.
See all 12 Language toolsReference
Symbols, notation, and quick lookups
Greek Alphabet
All 24 letters with names and uses.
Trig Identities
Pythagorean, double-angle, sum, and half-angle trig identities to copy.
Derivative Rules
Power, product, quotient, and chain rules plus common derivatives.
Integral Table
Common indefinite integrals and integration rules to copy.
Unit Circle
Angles in degrees and radians with sine, cosine, and tangent values.
Algebra Formulas
Quadratic formula, factoring, exponent, and logarithm rules to copy.
Geometry Formulas
Area, perimeter, surface area, and volume formulas for common shapes.
See all 19 Reference toolsMusic & Audio
Notes, tempo, intervals, and audio
Note to Frequency Calculator
Frequency of any musical note, and the nearest note to a frequency.
Tempo to Delay Calculator
Delay and note-value times in milliseconds from a tempo in BPM.
Musical Interval Calculator
Frequency ratio and cents between two notes or a semitone count.
Audio File Size Calculator
Uncompressed audio file size from sample rate, bit depth, and length.
Harmonic Series Calculator
Overtone frequencies of the harmonic series from a fundamental.
Music Transposition Calculator
Transpose a note or key by a number of semitones.
Cooking & Kitchen
Recipe scaling, conversions, and oven temps
Recipe Scaler
Scale recipe ingredients up or down by a factor or new serving size.
Cooking Measurement Converter
Convert between teaspoons, tablespoons, cups, millilitres, and ounces.
Oven Temperature Converter
Convert oven temperatures between Fahrenheit, Celsius, and gas mark.
Cups to Grams Converter
Convert cups to grams for flour, sugar, butter, and more.
Butter Converter
Convert butter between sticks, tablespoons, cups, grams, and ounces.
Air Fryer Converter
Adjust oven time and temperature for an air fryer.
Tools
Everyday academic utilities
Unit Converter
Length, mass, temperature, volume, and more.
Wheel of Names
Spin a wheel to pick a random winner.
Random Number & Picker
Random numbers or pick a name from a list.
Study Abroad Budget
Total cost of a program in one currency.
Markdown Editor
Write notes in Markdown, live preview.
Case Converter
UPPER, lower, Title, Sentence, camel, snake, kebab.
Color Converter
Convert between HEX, RGB, and HSL.
See all 10 Tools toolsTime & Date
Dates, durations, and time zones
Time Zone Converter
Convert a time between any two time zones.
Date Calculator
Days between dates, or add/subtract days.
Age Calculator
Exact age in years, months, and days.
Stopwatch & Timer
Stopwatch with laps and a countdown timer.
Business Days Calculator
Count working days (weekdays) between two dates.
Unix Timestamp Converter
Convert between Unix epoch time and a human date.
Week Number Calculator
Find the ISO week number for any date.
See all 11 Time & Date tools