About EnginStack

What EnginStack Is

EnginStack is a precision measurement reference built for engineers, machinists, architects, and anyone who works with physical quantities. We provide 269 unit converters across 18 measurement categories, each with the exact conversion formula, worked examples, a reference table, and engineering context explaining when and why the conversion matters in practice.

Every conversion constant embedded in our calculators is verified against official metrology definitions. We do not approximate. We do not round. The constants we use are the legal metrology definitions — from the 1959 International Yard and Pound Agreement to the 2019 redefinition of the kilogram — and the conversion math is exact to the precision of IEEE 754 double-precision floating point.

Who Builds EnginStack

EnginStack is written and maintained by the EnginStack Editorial Team — a small independent editorial operation, not a staffed consultancy. We do not claim credentials we cannot show you. What we do claim is a method, and every page gives you what you need to check it.

Each conversion constant is traced back to the document that legally defines it: the 1959 International Yard and Pound Agreement, the BIPM SI Brochure, NIST Special Publication 811, NIST Handbook 44, or the relevant national weights-and-measures statute. Each engineering case study is researched against the primary investigation record — the NASA Mishap Investigation Board reports, the NTSB and FAA dockets, the Lockwood Board of Inquiry — rather than against other people's summaries of them.

Where a source is a secondary summary rather than a primary record, we say so. Where two sources disagree on a figure, we say that too, and give the range. Where we simply do not know something, it stays out rather than being filled in with the most commonly repeated version. That last rule costs us words, and it is the one we care about most.

Every page gets a review pass before publication: each constant is re-derived from its definition, and each calculator's coefficient is tested in both directions against the site's own conversion engine to confirm it returns the exact reciprocal within floating-point limits. When a correction is needed — and in metrology, periodic corrections are inevitable as standards evolve — the page is updated and the change is noted.

Why EnginStack Exists

Search engines can answer “how many centimeters in an inch” — but they cannot tell you why the 1959 International Yard and Pound Agreement matters for your PCB design tolerances, or how unit conversion errors caused the loss of a $327 million Mars orbiter. That context is the value we add.

We created EnginStack after noticing that most online conversion tools give you a number and stop there. They do not explain the measurement history behind the constant, the engineering context in which the conversion matters, or the real-world consequences of getting it wrong. Every EnginStack converter page includes that context — from the Deepwater Horizon pressure conversion cascade to the MPG Illusion that tricks car buyers into misjudging fuel savings.

The site launched in 2025 with 60 converters and 4 pillar guides. It has since grown to 269 converters, 32 engineering guides, and 18 category reference hubs, all maintained to the same standard of metrological accuracy and engineering relevance.

Editorial Standards & Verification

Every conversion constant on EnginStack undergoes a three-step verification process:

1. Primary Source Check: The constant is traced to its originating metrology standard or international treaty. For example, the inch-to-millimeter ratio (25.4) is traced to the 1959 International Yard and Pound Agreement signed by the United States, United Kingdom, Canada, Australia, New Zealand, and South Africa.
2. NIST Cross-Reference: Where applicable, the constant is cross-referenced against NIST Special Publication 811 (Guide for the Use of the International System of Units) and NIST Handbook 44 (Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices).
3. Computational Verification: The conversion coefficient is tested in both directions using the site's calculator engine and verified to produce the exact reciprocal result within floating-point precision limits.

We do not claim professional licensure, standards-committee seats, or a staffed roster of practicing engineers. What we can show you is where every number came from. Where a page makes a factual claim about a historical event, that claim is checked against the primary investigation record and the source is named on the page. Where our sourcing is weaker than we would like, the page says so.

Measurement Standards We Use

The legal definitions that underpin every conversion on this site:

• Length: 1 inch = 25.4 mm exactly (International Yard and Pound Agreement, 1959). 1 foot = 0.3048 m. 1 mile = 1,609.344 m. 1 nautical mile = 1,852 m (International Hydrographic Organization). 1 astronomical unit = 149,597,870,700 m (IAU 2012 Resolution B2).
• Mass: 1 pound (avoirdupois) = 0.45359237 kg exactly (1959 Agreement). 1 ounce = 28.349523125 g. 1 ton (short) = 907.18474 kg. The kilogram itself was redefined in 2019 by fixing the Planck constant at 6.62607015 × 10⁻³⁴ J⋅s.
• Temperature: Celsius and Fahrenheit are affine scales defined by two fixed points: absolute zero (−273.15 °C, −459.67 °F) and the triple point of water (0.01 °C, 32.018 °F). The Kelvin is defined by fixing the Boltzmann constant k = 1.380649 × 10⁻²³ J/K.
• Pressure: 1 bar = 100,000 Pa exactly (not an SI unit but accepted for use). 1 atm = 101,325 Pa (standard atmosphere). 1 psi = 6,894.757293168 Pa. 1 torr = 1/760 atm. 1 mmHg = 133.322387415 Pa.
• Volume: 1 US liquid gallon = 231 cubic inches = 3.785411784 L (NIST Handbook 44, Appendix C). 1 imperial gallon = 4.54609 L (UK Weights and Measures Act 1985). 1 cup (US customary) = 236.5882365 mL.
• Area: 1 acre = 43,560 square feet (US survey). 1 hectare = 10,000 m². The US survey foot (1 ft = 1200/3937 m) was formally deprecated on January 1, 2023 by NIST, unifying all length-derived area measurements under the international foot.
• Energy & Power: 1 calorie (thermochemical) = 4.184 J. 1 kilowatt-hour = 3,600,000 J. 1 horsepower (mechanical) = 745.69987158227022 W. 1 BTU (IT) = 1,055.05585262 J.

How the Calculators Work

All computation runs in your browser via client-side JavaScript. Your input values never leave your device — we do not send data to any server, and we do not track your conversions. We use Google Analytics (GA4) exclusively to understand aggregate site traffic and page popularity; no personally identifiable information is collected, and GA4's default IP anonymization is enabled.

The calculator engine is a single shared JavaScript function that reads the conversion coefficient from each page's HTML data attributes and computes both forward and inverse results simultaneously. Temperature conversions use a specialized pathway to handle affine transformations (°C to °F) that require both multiplication and addition, unlike simple ratio conversions.

We deliberately avoid loading external libraries, frameworks, or third-party scripts beyond the Google Analytics snippet. The entire site is static HTML, CSS, and vanilla JavaScript, served from Cloudflare's global edge network. This architecture means pages load in under 500 milliseconds on a typical connection and remain usable offline once cached.

Engineering Guides

EnginStack publishes 31 engineering reference guides. Eighteen of them cover a measurement category in depth — the history, the metrology, the practical pitfalls. The rest split into applied guides for specific equipment and standards, and case studies of what happens when a conversion goes wrong. None of them are SEO filler; they exist to connect a conversion factor to a real engineering decision:

Category reference guides (18)

• Length — the 1959 yard-and-pound agreement, the 2023 retirement of the US survey foot, and why length errors have caused some of the most expensive engineering failures in history
• Weight & Mass — from the kilogram artefact in a Paris vault to the 2019 Planck-constant redefinition
• Area — acres, hectares, and why rounding error gets squared
• Volume & Cooking — the three-gallon problem: US liquid, US dry and imperial gallons differ by up to 20%
• Temperature — the only affine conversion most people use: Fahrenheit's brine-and-armpit origin, and why Celsius ran backwards
• Pressure — why pressure is the unit most likely to kill you: Deepwater Horizon, SCUBA cascade failures, Apollo 1
• Energy & Power — the kilowatt-hour problem: confusing kW with kWh is the most expensive unit mistake in engineering
• Force — newtons, pound-force, kilogram-force, and the three anchor constants the whole system rests on
• Torque — the 12× inch-pound trap, the 9.8× kilogram-meter trap, and why a newton-meter is not a joule
• Speed — Mach, knots and the speed of light: why runners and drivers disagree on “fast”
• Time — why a month isn't a real unit: leap seconds, the 7-day accident, and ISO 8601
• Density — why water anchors every unit, and the cubed-length trap that triples a unit error
• Flow Rate — L/min, GPM, m³/h, CFM, and the pump-sizing mistakes that follow from mixing them
• Electric — Ohm's and Watt's laws, the dBm power scale anchored at 30 dBm = 1 W, and AWG wire gauge
• Angle — degrees, radians, and the CSS spin that broke: why radians are the only honest angle
• Frequency — why 1 Hz = 60 RPM, and why the hertz is the only unit where every SI prefix conversion is exact
• Fuel Economy — the MPG Illusion: why a 10→20 MPG upgrade saves 3× more fuel than 30→60 MPG
• Data Storage — why 1 GB ≠ 1,024 MB (sometimes): the collision between binary addressing and decimal marketing

Applied guides (3)

• Air Conditioner Sizing — a “ton” of cooling is not a weight: 12,000 BTU/h, and how the ice trade created the unit
• Engine Displacement — cubic inches to litres, bore × stroke, and why the Ford 302 became the “5.0”
• The Year 2038 Problem — what happens when a 32-bit signed integer counts seconds out of room

Case studies (10)

• Mars Climate Orbiter — pound-force-seconds read as newton-seconds, and the observability gap that hid it for nine months
• Gimli Glider — 22,300 kg of fuel loaded as 22,300 lb, and a 17-minute dead-stick glide
• Concorde 4590 — a 43 cm strip of titanium alloy on the runway, and the takeoff arithmetic that followed
• Korean Air Cargo 6316 — an ATC clearance to 1,500 metres, read back as 1,500 feet
• Deepwater Horizon — 14 ppg of drilling mud, 3,300 feet of it displaced by seawater, and a 40% pressure drop
• The 1893 Photocopy — the Mendenhall Order, and how America's yard and pound became legal fractions of the metre
• The 1975 Metric Conversion Act — a voluntary law, and the US Metric Board that coordinated nothing before dissolving in 1982
• The Cost of Retooling — the 4 ft 8.5 in gauge, the Whitworth thread, and why retooling was physically impossible
• Why America Doesn't Use the Metric System — the 130-year history behind a measurement habit
• The 8 Most Expensive Unit Conversion Mistakes — the hub article that indexes the case studies above

Each guide is cross-linked into the wider collection, and each case study links back to the converter and the category guide that explains the physics behind it. Browse the full collection at the Engineering Guides hub.

Privacy Philosophy

EnginStack was built on the principle that a unit conversion tool should not require surveillance. Unlike many free converter sites that monetize through ad networks, cross-site tracking, or data brokerage, EnginStack carries no advertising, no affiliate links and no sponsorship; it is run as an independent editorial project. We use anonymous, aggregated analytics to understand which converters people find most useful — nothing more. For complete details, see our Privacy Policy.

Contact

To report a conversion error, suggest a new converter, or flag a sourcing problem: [email protected]. A correction that names the constant you believe is wrong, and the standard you are checking it against, gets acted on fastest. We would rather hear about an error than not hear about it.