Fraction arithmetic
Add, subtract, multiply or divide fractions and mixed numbers. See exact simplified results, common denominators and each calculation step.
Free calculators and developer tools
Use step-by-step math calculators and local developer utilities. See worked examples, formulas, input limits and sources without signing in.
Each page includes an interactive tool, a complete worked example, its method and limits, and links to the relevant reference material. Calculations and text conversion run in your browser. You do not need an Ithy account.
Math and statistics
Compare and order fractions
Compare two or more fractions, decimals and mixed numbers. Order them exactly and see the common-denominator explanation.
Decimal to fraction
Convert a finite decimal or scientific notation into a simplified fraction, with place-value and greatest-common-divisor steps.
Percentage calculator
Calculate a percent of a number, express one number as a percent of another, or find the whole from a known part and percentage.
Percentage change
Calculate relative percentage change, absolute change, multiplier and the reverse change. Distinguish percentage points from relative percent.
Ratio calculator
Simplify two positive decimal quantities to an exact whole-number ratio, then scale that ratio to a new first quantity.
Mean, median and mode
Find mean, median, all repeated modes, range, sum and a sorted list. See how an outlier changes the average compared with the middle value.
Standard deviation
Calculate sample and population variance and standard deviation together. See the mean, squared-deviation sum and the n versus n−1 denominator.
Weighted average
Calculate a weighted mean from value–weight pairs. See total weight, each weighted contribution and how percentage weights are normalized.
MAE, MSE, RMSE and R²
Compare actual and predicted values with per-row errors, MAE, MSE, RMSE and R². Handle constant targets and negative R² explicitly.
Binary, decimal and hex
Convert signed integers among binary, decimal, octal and hexadecimal without losing large integer digits. Check unsigned and two’s-complement 8-bit values.
Scientific notation
Convert a finite decimal or e notation into normalized scientific notation and an exact decimal expansion without rounding the entered digits.
Quadratic equation solver
Solve ax² + bx + c = 0, inspect the discriminant and vertex, and handle repeated, complex and linear cases explicitly.
Slope between two points
Calculate slope, rise, run, intercept, line equation and distance from two points. Handle vertical lines and identical points explicitly.
GCD and LCM
Find the greatest common divisor and least common multiple of signed whole numbers using exact integer arithmetic and Euclidean steps.
Pythagorean theorem
Find a hypotenuse or missing leg of a right triangle. See the squared-side equation, area and perimeter with explicit geometry assumptions.
Text, data and developer utilities
JSON formatter and validator
Validate and format JSON with two-space, four-space or compact output. Preserve numeric tokens, string escapes, key order and duplicate keys as written.
Base64 text encoder and decoder
Encode Unicode text as standard or URL-safe Base64. Decode valid Base64 back into UTF-8 text with explicit padding and invalid-byte checks.
URL encode and decode
Percent-encode a URL component or decode UTF-8 percent escapes. Choose literal-plus or form-plus interpretation explicitly.
Unix timestamp converter
Convert Unix seconds or milliseconds to UTC and browser-local time. Convert an ISO date-time with an explicit zone back to both timestamp units.
CSV and JSON converter
Convert header-based CSV into JSON objects or flat JSON objects into CSV. Preserve CSV text values and handle quoted commas, quotes and multiline fields.
Text and UTF-8 byte counter
Count UTF-8 bytes, Unicode code points, UTF-16 units, grapheme clusters, lines and whitespace-separated words. Inspect the difference with emoji.
HTML escape and entity decoder
Escape ampersands, angle brackets and quotes, or decode common named and numeric HTML entities once. Render results as text without a live HTML preview.
SHA-256 text checksum
Calculate a SHA-256 digest of UTF-8 text locally. Inspect byte count and compare a supplied hexadecimal checksum without uploading the input.
Research and engineering tools
Choose a tool by the question
Use fraction comparison to establish order, fraction arithmetic to calculate a result, and decimal conversion to express a finite decimal exactly. For percentages, identify whether you need a share of a total or a change from an earlier baseline. These questions use different denominators.
Statistics tools describe the values you supply. A small data set, a convenient average or a good fit does not by itself establish a cause or a reliable prediction. Keep the units, sampling process and evaluation split with your result.
Developer tools operate on text or bytes, depending on the format. UTF-8 byte counts differ from visible character counts, Base64 is reversible encoding, and a SHA-256 digest is a one-way checksum. For time conversion, select seconds or milliseconds explicitly and include a time zone in a date-time input.
A mathematics self-study roadmap · Sources and methodology · Report a specific error