Data Sources and Attribution

Government data

• U.S. Internal Revenue Service (IRS)

  U.S. government

  Federal income tax brackets and standard deductions, long-term capital gains rates, Social Security and Medicare tax rates, self-employment tax rules, 401(k) and IRA contribution limits, and the gift tax annual exclusion.

  Used in: Tax Bracket Calculator, Paycheck Calculator, Self-Employment Tax, Capital Gains Calculator, 401(k) Retirement Calculator, IRA Calculator, 529 Plan Calculator

  Tax rates and bracketsPublication 15Self-employment taxRetirement plan limitsCapital gains

• U.S. Social Security Administration (SSA)

  U.S. government

  The Social Security wage base, the yearly earnings limit for Social Security tax.

  Used in: Paycheck Calculator, Self-Employment Tax

  Contribution and benefit base

• U.S. Bureau of Labor Statistics (BLS)

  U.S. government

  Consumer Price Index for All Urban Consumers (CPI-U) annual averages, used to compare the buying power of a dollar between years.

  Used in: Inflation Calculator

  CPI homeCPI data

• State revenue departments

  U.S. state governments

  State sales tax base rates for the Sales Tax Calculator presets, and state income tax figures in the Paycheck Calculator. City, county and district taxes are not included, so rates are approximate.

  Used in: Sales Tax Calculator, Paycheck Calculator

Health and fitness formulas

These tools give general estimates, not medical advice. Talk to a qualified health professional about your own health.

• Body Mass Index categories

  World Health Organization

  Adult BMI categories: underweight below 18.5, healthy weight 18.5 to 24.9, overweight 25 to 29.9, and obesity 30 or above. The Ideal Weight Calculator also shows the weight range that gives a BMI of 18.5 to 24.9.

  Used in: BMI Calculator, Ideal Weight Calculator

  WHO: obesity

• Waist-to-hip ratio risk levels

  World Health Organization

  World Health Organization. Waist circumference and waist-hip ratio: report of a WHO expert consultation, Geneva, 8 to 11 December 2008. Published 2011.

  Used in: Waist-to-Hip Ratio

  WHO report

• Blood pressure categories

  American Heart Association

  Normal, elevated, stage 1 and stage 2 hypertension, and hypertensive crisis, as defined in the 2017 ACC/AHA blood pressure guideline.

  Used in: Blood Pressure Analyzer

  AHA: blood pressure readings

• Cholesterol ratio ranges

  AHA and NCEP

  Interpretation ranges for total cholesterol to HDL and LDL to HDL ratios, based on American Heart Association and National Cholesterol Education Program guidance.

  Used in: Cholesterol Ratio Calculator

• Mifflin-St Jeor equation (resting energy)

  Peer reviewed

  Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990;51(2):241-7. Combined with standard activity multipliers to estimate daily calories.

  Used in: Calorie & TDEE Calculator, Macro Calculator

• Compendium of Physical Activities (MET values)

  Peer reviewed

  Ainsworth BE, Haskell WL, Herrmann SD, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Medicine and Science in Sports and Exercise, 2011;43(8):1575-81.

  Used in: Calorie Burn Calculator

  Compendium website

• U.S. Navy circumference method (body fat)

  Research report

  Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984.

  Used in: Body Fat Calculator

• Ideal body weight formulas

  Published formulas

  Devine BJ (1974), Robinson JD and colleagues (1983), Miller DR and colleagues (1983), and Hamwi GJ (1964).

  Used in: Ideal Weight Calculator

• Lean body mass formulas

  Published formulas

  Boer P (1984), James WPT (1976) and Hume R (1966).

  Used in: Lean Body Mass Calculator

• One-rep max formulas

  Published formulas

  Epley B (1985), Brzycki M (1993) and Lander J (1985). The tool shows each estimate and their average.

  Used in: One Rep Max Calculator

• Maximum heart rate and the Karvonen method

  Published formulas

  Maximum heart rate estimated as 220 minus age (Fox SM, Naughton JP, Haskell WL, 1971). Training zones use heart rate reserve: Karvonen MJ, Kentala E, Mustala O. The effects of training on heart rate; a longitudinal study. Annales Medicinae Experimentalis et Biologiae Fenniae, 1957;35(3):307-15.

  Used in: Heart Rate Zones

• 3,500 calories per pound of body fat

  Peer reviewed

  Wishnofsky M. Caloric equivalents of gained or lost weight. American Journal of Clinical Nutrition, 1958;6(5):542-6. A rough rule; real weight change varies from person to person.

  Used in: Weight Loss Calculator

• Naegele's rule (due date)

  Clinical convention

  Estimated due date = first day of the last menstrual period + 280 days (40 weeks), adjusted for cycle length. The Ovulation Calculator uses the related assumption that ovulation happens about 14 days before the next period.

  Used in: Pregnancy Due Date Calculator, Ovulation Calculator

• Sleep cycles of about 90 minutes

  Peer reviewed

  Dement W, Kleitman N. Cyclic variations in EEG during sleep and their relation to eye movements, body motility, and dreaming. Electroencephalography and Clinical Neurophysiology, 1957;9(4):673-90.

  Used in: Sleep Calculator

• Alcohol units and standard drinks

  NHS and NIH

  One UK unit is 10 ml (8 g) of pure alcohol, so units = volume in ml x ABV / 1,000 (NHS). One US standard drink is 14 g of pure alcohol (National Institute on Alcohol Abuse and Alcoholism), using 0.789 g per ml of alcohol. This tool counts units and drinks only; it does not estimate blood alcohol concentration.

  Used in: Alcohol Units Calculator

  NHS: alcohol unitsNIAAA: standard drink

Readability

• Flesch Reading Ease and Flesch-Kincaid Grade Level

  Published formulas

  Flesch R. A new readability yardstick. Journal of Applied Psychology, 1948. Kincaid JP, Fishburne RP, Rogers RL, Chissom BS. Derivation of new readability formulas for Navy enlisted personnel. 1975.

  Used in: Reading Time Estimator

Standards and registries

• SI units and U.S. customary definitions

  BIPM and NIST

  Conversion factors follow the International System of Units (SI) and NIST's published definitions of U.S. customary units (for example, 1 inch = 2.54 cm and 1 pound = 0.45359237 kg), rounded to the precision each converter shows.

  Used in: Unit Converter, Length Converter, Weight Converter, Volume Converter, Temperature Converter

  BIPM: SI unitsNIST: unit conversion

• IANA Time Zone Database

  IANA

  Time zone rules and daylight saving changes come from the tz database built into your browser, which the tools read through the standard Intl date API.

  Used in: World Clock, Time Zone Converter, Unix Timestamp Converter

  IANA time zones

• IANA protocol registries

  IANA

  Port number ranges and service assignments, media (MIME) types, and DNS resource record types.

  Used in: Port Lookup, MIME Type Lookup, DNS Record Types

  Port numbersMedia typesDNS parameters

• IETF standards (RFCs)

  IETF

  HTTP status codes (RFC 9110), Base64 (RFC 4648), URL percent-encoding (RFC 3986), UUIDs (RFC 9562, which replaced RFC 4122), JSON Web Tokens (RFC 7519), CSV (RFC 4180), data URLs (RFC 2397), reserved example domains (RFC 2606) and IP subnets (CIDR, RFC 4632, and /31 links, RFC 3021).

  Used in: HTTP Status Codes, Base64 Encoder / Decoder, URL Encoder / Decoder, UUID Generator, JWT Decoder, CSV ↔ JSON Converter, Image to Base64 Converter, Email Generator, IP Subnet Calculator

  RFC 9110

• Unicode Standard

  Unicode Consortium

  Emoji characters, character code points, and Unicode normalization (used to separate letters from their accents).

  Used in: Emoji Picker, Emoji Remover, Accent Stripper

  The Unicode StandardEmoji list

• ASCII

  ANSI X3.4

  The 128-character US-ASCII code table.

  Used in: ASCII Table

• IEEE MAC address assignments (OUI)

  IEEE

  A small built-in list of common manufacturer prefixes from the IEEE Registration Authority. Prefixes not in the list are not identified.

  Used in: MAC Address Lookup

  IEEE Registration Authority

• International Morse code

  ITU

  Recommendation ITU-R M.1677-1, International Morse code.

  Used in: Morse Code Translator

  ITU-R M.1677-1

• Paper sizes

  ISO 216 and ANSI

  A4 (210 x 297 mm, ISO 216) and US Letter (8.5 x 11 in) page sizes in the tools that create PDFs and printable documents.

  Used in: Text to PDF, Image to PDF Converter, HTML to PDF, Invoice Generator, Letterhead Generator

  ISO 216

• Test numbers for developers

  Industry conventions

  Test card numbers use card network prefixes and the Luhn check digit (ISO/IEC 7812), so they pass format checks. They are for testing payment forms only and must never be used to pay for anything. U.S. test phone numbers use 555-0100 to 555-0199, which the North American Numbering Plan reserves for fictional use.

  Used in: Credit Card Test Generator, Phone Number Generator

Approximate reference values

These values are for quick reference. Check an official or live source before you rely on them.

• Clothing and jewelry size charts

  Approximate

  Conversions between US, UK, EU and other sizing systems are based on widely published industry tables. Sizing varies by brand, so check the maker's own size chart before you buy.

  Used in: Shoe Size Converter, Ring Size Converter, Hat Size Converter

• Currency exchange rates

  Approximate

  The Currency Exchange Rate Viewer uses fixed reference rates stored in the page. They are not live market data and are not updated automatically. Use your bank or a live rate provider for real transactions.

  Used in: Currency Exchange Rate Viewer

Quotes, word lists and sample text

• Quotations

  Public domain or anonymous

  Quotes are credited as they are commonly attributed, mostly to authors whose works are in the public domain or to Anonymous. Attributions for popular sayings can be uncertain. If you think a quote is misattributed, please tell us.

  Used in: Random Quote Generator

• Word and name lists

  Built into each tool

  Short lists of everyday English words, first names, surnames and place names built into each tool. Generated names, usernames and addresses are random combinations and are not meant to describe real people or places.

  Used in: Random Word Generator, Name Generator, Username Generator, Fake Data Generator, Address Generator

• Lorem ipsum

  Public domain

  Traditional placeholder text adapted from Cicero's De finibus bonorum et malorum (45 BC).

  Used in: Lorem Ipsum Generator

Accuracy and updates