SC QUALITY GUILDSI and metrology unit converter
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Convert between SI and US customary units with the exact defining factors, and see the value in every unit at once. Also: SI prefixes, scientific and engineering notation, degrees-minutes-seconds, percent and ppm, and decibels.
ON THE EXAM · CCT I.A, I.B, I.C, IV.D.1, IV.D.2, IV.D.3, IV.D.8 · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
Q-BotClick for an explanation of this tool.For educational use. This page is a study aid. The method behind it has far more depth and detail than one page and one tool can cover, and what you see here is not everything the method offers or everything this site offers. For full understanding and application, use the governing standards and texts, and seek further education, training or qualified advice. Results depend on the data you enter, so check them before relying on them.
Why exact factors matter
Most conversion factors used in calibration are exact by definition, not measured. Since 1959 the inch has been exactly 25.4 mm and the pound exactly 0.45359237 kg. Standard gravity is exactly 9.80665 m/s². Everything else follows from those: a pound-force is 0.45359237 × 9.80665 = 4.4482216152605 N, and a psi is that force over one square inch, about 6894.757 Pa. A converted value is only as good as the factor you used, so a factor rounded to three figures can add an error larger than the instrument's own. This tool builds every factor from the definitions in NIST Special Publication 811, Appendix B, and marks the few that are conventional rather than exact: the manometric pressure units such as mmHg and inH2O, and the calorie and Btu.
The SI in brief
- Seven base units: meter, kilogram, second, ampere, kelvin, mole and candela. Since 2019 each is defined by fixing the value of a constant of nature.
- Derived units are products and quotients of base units: the newton is kg·m/s², the pascal N/m², the joule N·m, the watt J/s.
- Prefixes scale a unit by a power of ten, from quecto (10−30) to quetta (1030). Symbols are case sensitive: m is milli, M is mega. Going from mega to kilo moves the decimal point three places to the right.
Temperature is the odd one
Celsius, Fahrenheit and kelvin have different zeros, so a temperature reading converts with an offset: °F = °C × 9/5 + 32. A temperature difference does not. A tolerance of ±2 °C is ±3.6 °F, not ±35.6 °F. Uncertainties, drifts and tolerances are differences, so use the temperature-difference units for them.
Torque and energy
A pound-force foot of torque and a foot pound-force of energy have the same dimensions but are different quantities. The tool keeps them apart, and in the worksheet a symbol such as ft-lb is read as whichever one the other unit in the row belongs to.
Notation, angles and ratios
- Scientific notation puts one digit before the decimal point: 4.5670 × 10−5. Engineering notation keeps the exponent a multiple of three, so it reads straight off as an SI prefix: 45.670 × 10−6 A is 45.670 µA.
- Angles: one degree is 60 minutes, one minute 60 seconds. A full turn is 360°, 2π radians and 400 grads.
- Ratios: 1% is 10,000 ppm. Decibels are logarithmic: 10 log10 of a power ratio, or 20 log10 of an amplitude ratio such as voltage. Doubling the power is +3 dB; doubling the voltage is +6 dB.
On the exam
The CCT Body of Knowledge asks you to define the seven base units (I.A), calculate and convert derived units (I.B) and use the SI multipliers, for example mega to kilo and micro to milli (I.C). In applied mathematics it lists scientific and engineering notation (IV.D.1), English and metric conversions of length, area, volume, capacity and mass (IV.D.2), percentage, ppm and decibels (IV.D.3) and angular conversions between degrees, minutes, seconds, grads and radians (IV.D.8). Expect calculator questions where a factor or an offset applied the wrong way round is the trap.