Sources by type
| Source type | Citations | Share | Distinct domains |
|---|---|---|---|
| Government & regulatory agency | 40 | 27% | 21 |
| International standards body | 17 | 11% | 9 |
| Peer-reviewed research | 16 | 11% | 10 |
| Reference work or industry source | 76 | 51% | 47 |
| Total | 149 | 100% | 87 |
Counts recompute at every build from the same source list each calculator page cites, so they track the site as new tools are added.
What counts as each type
Government & regulatory agency covers federal and foreign agencies that publish the rule or table a calculator applies directly: the CDC's adult BMI cutoffs, the CFPB's mortgage amortization method under Regulation Z, the FDIC's deposit insurance limits, the Iowa DOT's asphalt density spec.
International standards body covers organizations that define the unit or format itself, not one country's application of it: BIPM for the metric system, IUPAC for chemistry nomenclature, the Unicode Consortium, ECMA International, the International Code Council, IANA's time zone database, College Board for SAT scoring.
Peer-reviewed research covers calculators built on a named, dated study: the Mifflin-St Jeor resting-energy equation (1990), the Mosteller and Du Bois body-surface-area formulas, Woods et al.'s 2015 reaction-time study, Hoeger et al.'s 2008 step-length regression.
Reference work or industry source covers everything else with a checkable citation: Wikipedia, Britannica, Wolfram MathWorld, and manufacturer or trade documents like QUIKRETE's technical data sheet or the Asphalt Institute's density range. These mostly back descriptive or historical claims: how a symbol got its shape, what a lumber grade means. None of them set a regulated number.
Finance
Tip Calculator
- Reference The Emily Post Institute — "Tipping Etiquette 101: A Comprehensive Guide on Tipping" (US tip percentages by service)
- Government UK Government legislation — Employment (Allocation of Tips) Act 2023 (legal requirement to pass tips to workers in full)
- Government French Ministry for the Economy (DGCCRF) — "Pourboire" (service compris legally included in menu prices since 1987)
- Government Japan Travel (official Japan National Tourism Organization site) — "Tipping in Japan"
- Government Fair Work Ombudsman (Australian Government) — national minimum wage rates
- Reference Lonely Planet — "Tipping customs in Asia" (mainland China conventions)
- Reference Cathay Pacific — "A complete guide to tipping in the Chinese Mainland" (tour guides as the common exception)
- Government U.S. Department of Labor, Wage and Hour Division — Fact Sheet #15A: Ownership of Tips Under the FLSA
- Reference Tax Foundation — 2026 State Sales Tax Rates (range and population-weighted average)
Home Improvement
Pool Calculator
- Reference Hayward Inc., "Aqua Rite Electronic Chlorine Generator, Operation and Installation Manual" (2,700-3,400 ppm ideal salt range, 3,200 ppm optimal target, gallons-by-shape formulas including the oval 6.7 multiplier, Check Salt/High Salt warning thresholds)
- Government NIST Handbook 44, Appendix C, General Tables of Units of Measurement (exact US gallon = 231 in³, exact cubic foot = 1,728 in³, exact avoirdupois pound = 453.59237 g)
Construction
Stair Calculator
- Standards body 2021 IRC R311.7.5: stair risers, treads and dimensional limits (ICC)
- Standards body ICC: International Residential Code overview
Board Foot Calculator
- Peer-reviewed University of Wisconsin-Madison Division of Extension, Forestry, FEM-042 — "What Is A Board Foot?" (the sawed-lumber board-foot formula and definition)
- Reference Wikipedia — "Board foot" (definition and formula, for general corroboration)
- Government NIST — DOC Voluntary Product Standard PS 20-20, "American Softwood Lumber Standard"
- Reference Rockler — "What Does the Quarter System of Lumber Thickness Mean?"
Asphalt Calculator
- Government Iowa Department of Transportation: Standard Specifications, Section 2303, "Hot Mix Asphalt Mixtures" (145 lb/ft³ unit weight for tonnage conversion)
- Reference Asphalt Institute: Engineering FAQs (142-148 lb/ft³ in-place density range for asphalt mixture)
- Government Federal Highway Administration: FHWA-RD-97-148, "User Guidelines for Waste and Byproduct Materials in Pavement Construction," Reclaimed Asphalt Pavement material description (100-125 lb/ft³ compacted density range)
- Reference Colorado Asphalt Pavement Association: "A Paving Fundamental: Thickness-Yield-Smoothness," compiled by James Scherocman, P.E. (loose lift vs. compacted thickness factor)
Topsoil Calculator
- Reference SDSU Extension (Hans Klopp & Anthony Bly), "Bulk Density is an Indicator of Soil Health," updated September 22, 2023 (tabulates USDA NRCS Soil Health Educators Guide 2023 ideal bulk-density ceilings by soil texture)
- Reference University of Maryland Extension, "Starting a New Lawn" (4-6 in till depth for soil amendments)
- Reference University of Maryland Extension, "Soil to Fill Raised Beds" (8 in and 12-24 in depth minimums, 20% topsoil-by-volume guidance)
Education
SAT Score Calculator
- Standards body College Board: Scoring Your Paper SAT Practice Test #4 (PDF, © 2023)
- Standards body College Board: SAT practice tests
Words to Pages Calculator
- Reference William Shunn, "Proper Manuscript Format": the 12-point, double-spaced formatting convention this calculator uses as its baseline
- Reference William Shunn, "The Old Rule of Thumb for Estimating Word Count Is Obsolete": why a page-based word count is an estimate, not a substitute for your word processor's exact count
- Reference Purdue OWL: MLA General Format, the 12-point font and double-spacing convention for academic papers
Science
Molarity Calculator
- Standards body IUPAC Gold Book: amount concentration
- Government PubChem (NIH): compound molar masses
Health
Calorie Calculator
- Peer-reviewed Mifflin MD, St Jeor ST, et al., "A new predictive equation for resting energy expenditure in healthy individuals," American Journal of Clinical Nutrition 1990;51(2):241-247
- Peer-reviewed 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults (Circulation)
- Government NIDDK: NIH Body Weight Planner (Diabetes Discoveries & Practice Blog, Kevin D. Hall)
Steps to Miles Calculator
- Peer-reviewed Hoeger, W.W.K. et al., "One-Mile Step Count at Walking and Running Speeds," ACSM's Health & Fitness Journal, Vol. 12, No. 1, pp. 14-19 (2008) — source of the 0.415 (men) / 0.413 (women) step-length-to-height regression
- Government CDC/NCHS, "Body Measurements" (FastStats) — U.S. average adult height, ages 20+, NHANES 2021-2023
Body Surface Area (BSA) Calculator
- Peer-reviewed Du Bois D, Du Bois EF, "A formula to estimate the approximate surface area if height and weight be known," Archives of Internal Medicine 17(6):863-871 (1916)
- Peer-reviewed Mosteller RD, "Simplified calculation of body-surface area," New England Journal of Medicine 317(17):1098 (1987)
- Peer-reviewed National Kidney Foundation, "Frequently Asked Questions About GFR Estimates" (2022), Q6 (1.73 m² indexing, Du Bois formula) and Q44 (indexed vs. non-indexed eGFR for drug dosing)
Games
Click Speed Test
- Peer-reviewed Ruff, R.M. & Parker, S.B. (1993). "Gender- and age-specific changes in motor speed and eye-hand coordination in adults: normative values for the Finger Tapping and Grooved Pegboard Tests," Perceptual and Motor Skills, 76, 1219-1230
- Reference Millisecond — "Finger Tapping Test" test library (protocol description, citing Halstead, 1947, and Reitan & Wolfson, 1985)
Conversion
Volume Converter
- Government NIST Handbook 44 (2026), Appendix C — General Tables of Units of Measurement
- Government U.S. Energy Information Administration — Glossary (Barrel)
- Reference Sizes, Inc. — "English wine gallon" (1707 231 in³ standard; US 1836 adoption; UK 1824 Imperial gallon split)
- Government eCFR — 27 CFR § 5.203, Standards of Fill (Container Sizes), TTB
Electrical Converter (Watts, Amps, Volts)
- Reference Wikipedia — "Ohm's law" (voltage, current, resistance relationship)
- Reference Wikipedia — "Electric power" (P = V x I and power in AC circuits)
- Reference Wikipedia — "Power factor" (real vs. apparent power in AC circuits)
- Reference Wikipedia — "Three-phase electric power" (line-to-line vs. line-to-neutral formulas)
- Reference Wikipedia — "IEC 60038" (standard mains voltages by region)
Math
Fraction Calculator
- Standards body Common Core State Standards for Mathematics, Grade 5 Number and Operations, Fractions domain (5.NF.A.1, 5.NF.B.4)
- Standards body Common Core State Standards for Mathematics, Grade 6 The Number System (6.NS.A.1): dividing any fraction by any fraction
- Peer-reviewed Euclid, Elements, Book VII, Proposition 2: the Euclidean algorithm for the greatest common divisor
Rounding Calculator
- Reference Wikipedia — "Rounding" (tie-breaking rules and directed-rounding definitions)
- Reference Wikipedia — "IEEE 754" (round-to-nearest-ties-to-even as the binary default)
- Reference ASTM International — "How Do You Round Fractions? Significant Digits and Converting to a Decimal" (ASTM E29 practice)
Date & Time
Date Calculator
- Government 5 U.S.C. § 6103, Thanksgiving Day fixed as the fourth Thursday in November (Cornell Legal Information Institute)
- Standards body ECMA-262, the ECMAScript Language Specification, §21.4 "Date Objects" (proleptic Gregorian calendar convention)
- Reference Microsoft Support, "DATEDIF function," Excel (the year/month/day breakdown convention this calculator follows)
World Clock & Time Zone Converter
- Standards body IANA Time Zone Database (tzdata): the authoritative source for UTC offset and daylight-saving rules this page reads live via the browser's Intl API
- Standards body ECMA-402, the ECMAScript Internationalization API Specification: defines Intl.DateTimeFormat's time-zone-aware formatting behavior
- Reference Wikipedia — "Daylight saving time in Iran" (Iran's abolition of DST, effective September 2022)
- Reference Wikipedia — "Time in India" (the 1906 adoption of UTC+5:30 as a compromise between two proposed one-hour zones)
- Reference timeanddate.com — "Time Zone & Clock Changes in Lord Howe Island" (the island's 30-minute daylight-saving shift)
Age Difference Calculator
- Reference Wikipedia — "Age disparity in sexual relationships," §"Half-your-age-plus-seven" rule
- Reference xkcd #314, "Dating Pools" (2007) — origin of the "Standard Creepiness Rule" phrasing
- Reference Pew Research Center — "A growing share of U.S. husbands and wives are roughly the same age" (Aug. 2024), analysis of U.S. Census Bureau data
Food & Drink
Keg Calculator
- Government 27 CFR § 25.11, Definition of "barrel" (31 US gallons), eCFR (Electronic Code of Federal Regulations)
- Government 27 CFR § 25.156, Determination of tax on keg beer (authorized keg fractions and metric sizes), eCFR
- Government National Institute on Alcohol Abuse and Alcoholism, "What Is A Standard Drink?" (12 oz beer at ~5% ABV reference)
- Reference Siebel Institute of Technology, "How much does wasting draught beer cost a Retailer?" (draft-beer waste range)
Pizza Calculator
- Reference PMQ Pizza — "Pizza Slice Cutting Guide" (PMQ Think Tank, the pizza industry trade forum) — small/medium/large slice-count convention
- Reference PMQ Pizza — "Can Cutting Pizzas into Bigger Slices Save Labor Costs?" (documented example of a chain changing its slice count)
- Reference Pizza Hut — Office & Corporate Lunch Catering (official group-ordering guidance, the "Rule of 3")
Text Tools
Sentence Counter
- Peer-reviewed Flesch, R. (1948), "A New Readability Yardstick," Journal of Applied Psychology, 32(3), 221-233 (source of the Reading Ease formula and its 206.835/1.015/84.6 constants)
- Reference Kincaid, J. P., Fishburne, R. P., Rogers, R. L., & Chissom, B. S. (1975), "Derivation of New Readability Formulas (Automated Readability Index, Fog Count and Flesch Reading Ease Formula) for Navy Enlisted Personnel," Research Branch Report 8-75, Chief of Naval Technical Training, Naval Air Station Memphis (source of the Flesch-Kincaid Grade Level formula, via Defense Technical Information Center / Internet Archive)
- Peer-reviewed Brysbaert, M. (2019), "How many words do we read per minute? A review and meta-analysis of reading rate," Journal of Memory and Language, 109
- Reference ReadabilityFormulas.com, "Learn About the Flesch Reading Ease Formula" (score-band interpretation table)
Words Per Minute (WPM) Average Calculator
- Reference Arif & Stuerzlinger (2009), "Analysis of Text Entry Performance Metrics," IEEE TIC-STH '09 (WPM formula and the 5-character-per-word convention)
- Peer-reviewed Karat, Halverson, Horn & Karat (1999), CHI '99 Proceedings, ACM (average computer user typing speeds)
- Peer-reviewed Palin, Feit, Kim, Kristensson & Oulasvirta (2019), MobileHCI '19 Proceedings, ACM (37,000-participant mobile typing study)
- Reference Wikipedia: "Words per minute" (independent cross-check of the formula, convention, and cited figures)
- Reference Guinness World Records: "Fastest realtime court reporter (stenotype writing)"
Real Estate
Tech
Sports
Golf Club Distance Chart
- Reference TrackMan — "What is Club Speed?" (average amateur and Tour clubhead speed/distance data)
- Reference Golf.com — "This is how far PGA and LPGA Tour players hit it with every club"
- Reference PlayBetter — "Golf Club Distance Charts for Men and Women" (skill-level distance chart)
- Reference MyGolfSpy — "Golf Club Gapping Tool" (healthy gap-range guidance)