Precision Converters & Engineering Reference
200+ precision unit converters backed by international metrology standards. Every constant verified, every formula explained, no approximations — exact constants only.
Popular Conversions
The most-used converters, one click away. Every factor is exact — no approximations.
| From | To | Factor | |
|---|---|---|---|
| Inches | Centimeters | 1 in = 2.54 cm | Convert — |
| Fahrenheit | Celsius | °C = (°F — 32) × 5/9 | Convert — |
| Pounds | Kilograms | 1 lb = 0.45359237 kg | Convert — |
| Miles | Kilometers | 1 mi = 1.609344 km | Convert — |
| Gallons (US) | Liters | 1 gal = 3.78541 L | Convert — |
| Minutes | Hours | 60 min = 1 hr | Convert — |
| Acres | Square Feet | 1 acre = 43,560 sq ft | Convert — |
| Cups | Milliliters | 1 cup = 236.588 mL | Convert — |
| Degrees | Radians | 180° = π rad | Convert — |
The 8 Most Expensive Unit Conversion Mistakes in Engineering History
$327M Mars Climate Orbiter. 28 soldiers at Dhahran. A warship that capsized in 20 minutes. A bridge built to the wrong sea level. 8 disasters where one unconverted number cost billions — with root-cause diagrams and the habits that would have prevented every one of them.
Read the article →Length Conversion: The Complete Engineering Guide
Exact constants, 1,000 years of measurement history, systematic pitfalls across 5 engineering disciplines, and the real-world cost of unit conversion failures — from the Mars Climate Orbiter to the Gimli Glider.
Read the guide →Pressure Conversion Guide — From Vacuum to Gigapascals
Why pressure is the unit most likely to kill you. Every pressure unit — pascal, bar, psi, atm, torr — their origins and exact conversions. Deepwater Horizon, SCUBA cascade failures, and the Apollo 1 fire.
Read the guide →Energy & Power Conversion Guide — The Kilowatt-Hour Problem
Why confusing kW and kWh is the most expensive unit mistake in engineering. Watts, horsepower, joules, calories — exact constants, the story behind each unit, and the real cost of confusing a rate for a quantity.
Read the guide →Temperature Conversion Guide — °F, °C, Kelvin
Temperature is the only affine conversion most people use. Fahrenheit's brine-and-armpit origin, why Celsius ran backwards until Linnaeus flipped it, the 1851 body temperature myth that survived 141 years, and why every engineering pipeline converts to Kelvin first.
Read the guide →Volume & Cooking Conversion Guide — The Three-Gallon Problem
Three different gallons, four different cups, and a 20% fuel error waiting at 35,000 feet. From French baking recipes to concrete pours to Olympic swimming pools — every volume unit catastrophe starts with assuming a word means the same thing everywhere.
Read the guide →Data Storage Conversion Guide — Why 1 GB ≠ 1,024 MB (Sometimes)
Why your 1 TB hard drive shows 931 GB. Binary addressing vs decimal marketing — a 66-year naming collision. The class-action lawsuits, the IEC standard nobody adopted, and why Windows and macOS give different file sizes for the same byte count.
Read the guide →Speed Conversion Guide — Why 1 mph Isn’t Quite 1.609 km/h
The exact 1.609344 constant, the Mach and light-speed scale, why runners and drivers disagree on “fast,” and the unit mix-up that helped doom a Mars mission. From feet-per-second to knots to the speed of sound.
Read the guide →Time Conversion Guide — The 7-Day Accident and the 30-Day Lie
Why a month isn’t a real unit, how leap seconds nearly broke the internet, and the calendar math that quietly inflates every subscription. From the Babylonian week to ISO 8601.
Read the guide →Area Conversion Guide — Acres, Hectares & Square Feet
Why area is length squared — and why early rounding error gets squared too. The acre (43,560 ft² from oxen and a plough), the hectare (10,000 m² the world farms in), the square-foot-to-square-meter code gap, and the 2023 US survey-foot retirement that moved every surveyed acre by a few parts per million.
Read the guide →Weight & Mass Conversion Guide — Pounds, Ounces, Grams & Tonnes
Why the kilogram used to be a physical artefact in a Paris vault, how a mass-unit mismatch helped lose a Mars lander, and the everyday traps in pounds, ounces, grams, and tonnes — from carats to container ships.
Read the guide →Angle Conversion Guide — Degrees, Radians & the CSS Spin That Broke
Why radians are the only honest angle, what the gradian was for, and how a wrong-degree unit silently breaks CSS rotate(), game-engine rotations, and CNC rotary axes. From the Babylonian 360 to the 400-gon French circle.
Read the guide →Fuel Economy Conversion Guide — MPG, L/100km & the MPG Illusion
Why a 10→20 MPG upgrade saves 3× more fuel than 30→60 MPG. The MPG Illusion that tricks every car buyer, the US vs Imperial gallon trap, the 235.215 constant, and why Europe switched to L/100km for a reason — fuel economy is the only unit where "higher is better" makes math lie to you.
Read the guide →