Compendium

Engineering Units & Conversions — Family Index

17 min read

Engineering Units & Conversions — Family Index

1. At a glance

The Système International d’Unités (SI) is the modern, coherent, decimal-based system of units maintained by the Bureau International des Poids et Mesures (BIPM, Sèvres, France) and adopted globally under the Metre Convention of 20 May 1875. The current form was established by the 11th CGPM in 1960 as the SI proper. The most consequential modern revision is the 2019 SI redefinition (effective 20 May 2019, World Metrology Day), in which the kilogram, ampere, kelvin, and mole were redefined by fixing the numerical values of seven defining constants of nature:

ConstantSymbolFixed value
caesium hyperfine frequencyΔν_Cs9 192 631 770 Hz
speed of light in vacuumc299 792 458 m/s
Planck constanth6.626 070 15 × 10⁻³⁴ J·s
elementary chargee1.602 176 634 × 10⁻¹⁹ C
Boltzmann constantk1.380 649 × 10⁻²³ J/K
Avogadro constantN_A6.022 140 76 × 10²³ mol⁻¹
luminous efficacy (540 THz)K_cd683 lm/W

The redefinition eliminated the kilogram’s dependence on Le Grand K — the platinum-iridium artifact at the BIPM whose mass had drifted detectably (~50 µg over a century) relative to its sister copies. Mass is now traceable via the Kibble (watt) balance through h. The vacuum permeability µ₀ is no longer exactly 4π × 10⁻⁷ H/m; it is a measured quantity with uncertainty inherited from the fine-structure constant α (numerically µ₀ ≈ 1.256 637 062 × 10⁻⁶ H/m).

Engineering practice spans SI (global, official) and customary (US, UK imperial, gauge-based shop conventions). Drawings, codes, and contracts mandate explicit unit declaration; mixed-unit calculations are the dominant source of numerical errors (Mars Climate Orbiter, 1999 — lbf·s vs N·s).

2. Seven SI base units (post-2019)

All seven are defined by fixed numerical values of physical constants — no artifact, no material standard, no prototype. Definitions are mise en pratique via the corresponding constant.

  • second (s) — duration of 9 192 631 770 periods of the radiation from the ground-state hyperfine transition of ¹³³Cs (unperturbed). Realized by primary caesium fountain clocks; secondary optical-lattice clocks (Sr, Yb) provide higher accuracy (~10⁻¹⁸).
  • metre (m) — distance light travels in vacuum in 1/299 792 458 s. Realized by stabilized lasers (633 nm HeNe, 532 nm Nd:YAG/iodine).
  • kilogram (kg) — fixed by h = 6.626 070 15 × 10⁻³⁴ kg·m²/s. Realized by Kibble balance (electromagnetic force vs gravitational) and by X-ray crystal density (silicon-28 sphere) Avogadro route.
  • ampere (A) — fixed by e = 1.602 176 634 × 10⁻¹⁹ C; one ampere is the flow of 1/e elementary charges per second. Realized by single-electron pumps and via Josephson + quantum Hall (V and Ω).
  • kelvin (K) — fixed by k = 1.380 649 × 10⁻²³ J/K. Realized by acoustic gas thermometry, dielectric-constant gas thermometry, Johnson noise thermometry; legacy realization at triple point of water (273.16 K) retained as a reference fixed point.
  • mole (mol) — contains exactly 6.022 140 76 × 10²³ specified elementary entities. Decoupled from kilogram-of-¹²C definition.
  • candela (cd) — luminous intensity in a given direction of a source emitting monochromatic 540 × 10¹² Hz radiation with radiant intensity 1/683 W/sr. Realized by cryogenic radiometers + photometric integrating spheres.

3. SI prefixes

Decimal multiples and submultiples. The CGPM in November 2022 added four new prefixes (ronna, quetta, ronto, quecto) to support data-storage scales now reaching 10²⁷ B.

PrefixSymbolFactorPrefixSymbolFactor
quectoq10⁻³⁰decada10¹
rontor10⁻²⁷hectoh10²
yoctoy10⁻²⁴kilok10³
zeptoz10⁻²¹megaM10⁶
attoa10⁻¹⁸gigaG10⁹
femtof10⁻¹⁵teraT10¹²
picop10⁻¹²petaP10¹⁵
nanon10⁻⁹exaE10¹⁸
microµ10⁻⁶zettaZ10²¹
millim10⁻³yottaY10²⁴
centic10⁻²ronnaR10²⁷
decid10⁻¹quettaQ10³⁰

Stacking is forbidden (no “mµm”); kilogram is the one base unit with a prefix, so multiples are derived from gram (Mg, not kkg). Binary IEC prefixes (kibi Ki = 2¹⁰, mebi Mi = 2²⁰, gibi Gi = 2³⁰, …, yobi Yi = 2⁸⁰) are distinct and apply only to information units.

4. Common derived units

Coherent derived units constructed from base units; named ones honor the discoverer.

QuantityUnitSymbolIn base units
frequencyhertzHzs⁻¹
forcenewtonNkg·m·s⁻²
pressure / stresspascalPakg·m⁻¹·s⁻² (N/m²)
energy / workjouleJkg·m²·s⁻² (N·m)
powerwattWkg·m²·s⁻³ (J/s)
electric chargecoulombCA·s
electric potentialvoltVW/A (J/C)
capacitancefaradFC/V
resistanceohmΩV/A
conductancesiemensSA/V (Ω⁻¹)
magnetic fluxweberWbV·s
magnetic flux densityteslaTWb/m²
inductancehenryHWb/A
Celsius temperature°C°CK (offset 273.15)
luminous fluxlumenlmcd·sr
illuminanceluxlxlm/m²
activity (radionuclide)becquerelBqs⁻¹
absorbed dosegrayGyJ/kg
dose equivalentsievertSvJ/kg (weighted)
catalytic activitykatalkatmol/s

5. Length

  • 1 in = 25.4 mm (exact, defined 1959 international inch)
  • 1 ft = 12 in = 0.3048 m (exact)
  • 1 yd = 3 ft = 0.9144 m (exact)
  • 1 statute mi = 5280 ft = 1609.344 m (exact)
  • 1 nautical mi (international) = 1852 m (exact)
  • 1 fathom = 6 ft = 1.8288 m
  • 1 furlong = 220 yd = 201.168 m
  • 1 rod (perch) = 16.5 ft = 5.0292 m
  • 1 chain (Gunter’s) = 66 ft = 20.1168 m
  • 1 thou / mil = 0.001 in = 25.4 µm
  • 1 micron (µm) = 10⁻⁶ m
  • 1 Ångström (Å) = 10⁻¹⁰ m = 0.1 nm

Astronomical: 1 AU = 149 597 870 700 m (exact, IAU 2012); 1 light-year = 9.460 730 472 580 800 × 10¹⁵ m (exact by definition of year as Julian); 1 parsec = 648 000/π AU ≈ 3.085 677 581 × 10¹⁶ m.

Typesetting (printer’s measure): 1 PostScript point = 1/72 in = 0.352 778 mm; 1 pica = 12 PostScript points = 4.233 mm; 1 didot point (European) = 0.376 mm; 1 cicero = 12 didots = 4.512 mm.

6. Area

  • 1 in² = 6.4516 cm² (exact); 1 ft² = 0.092 903 04 m²; 1 yd² = 0.836 127 36 m²
  • 1 acre = 43 560 ft² = 4840 yd² = 4046.8564 m²
  • 1 hectare (ha) = 10 000 m² = 0.01 km² = 2.471 054 acres
  • 1 mi² = 640 acres = 2.589 988 km²
  • 1 are (a) = 100 m²
  • 1 sq mil = 10⁻⁶ in² = 6.4516 × 10⁻¹⁰ m²
  • 1 circular mil (cmil) = (π/4) × (mil)² = 5.067 × 10⁻¹⁰ m² (wire gauge: 1 AWG cross-section in cmil)
  • 1 barn (nuclear cross section) = 10⁻²⁸ m² = 100 fm²

7. Volume

  • 1 L = 10⁻³ m³ = 1 dm³; 1 mL = 1 cm³
  • 1 m³ = 1000 L = 35.3147 ft³ = 264.172 US gal
  • 1 ft³ = 28.3168 L = 0.028 316 846 m³ (exact 1728 in³)
  • 1 yd³ = 0.764 555 m³
  • 1 US gal (liquid) = 231 in³ (exact) = 3.785 411 784 L
  • 1 UK (imperial) gal = 4.546 09 L (exact)
  • 1 US qt = 0.946 353 L; 1 US pt = 0.473 176 L
  • 1 US fl oz = 29.5735 mL; 1 UK fl oz = 28.4131 mL
  • 1 cup (US legal, FDA) = 240 mL; 1 cup (US customary) = 236.588 mL
  • 1 tbsp (US) = 14.7868 mL; 1 tsp (US) = 4.9289 mL
  • 1 bbl (US petroleum, oil) = 42 US gal = 158.987 L
  • 1 bbl (US dry) = 115.6 L; 1 bbl (US liquid) = 119.24 L
  • 1 acre-ft = 1233.482 m³ (irrigation, hydrology)
  • 1 board-ft = 144 in³ = 2360 cm³ (lumber)

8. Mass / weight

  • 1 oz (avoirdupois) = 28.349 523 125 g (exact)
  • 1 lb (avoirdupois) = 16 oz = 0.453 592 37 kg (exact, since 1959)
  • 1 short (US) ton = 2000 lb = 907.184 74 kg
  • 1 long (UK) ton = 2240 lb = 1016.046 9 kg
  • 1 metric ton (tonne, t) = 1000 kg = 2204.62 lb
  • 1 grain (gr) = 64.798 91 mg (1/7000 lb avoirdupois)
  • 1 oz troy (precious metals) = 31.103 4768 g
  • 1 lb troy = 12 oz troy = 373.2417 g
  • 1 carat (metric, gemstones) = 200 mg = 0.2 g (exact)
  • 1 slug = 14.593 903 kg (mass that accelerates 1 ft/s² under 1 lbf)
  • 1 stone (UK) = 14 lb = 6.350 29 kg
  • 1 hundredweight (US cwt) = 100 lb = 45.359 kg
  • 1 hundredweight (UK long cwt) = 112 lb = 50.802 kg

9. Force

  • 1 N = 1 kg·m/s² (force giving 1 kg an acceleration of 1 m/s²)
  • 1 lbf (pound-force) = 4.448 222 N (force of standard gravity on 1 lb mass)
  • 1 kgf (kilogram-force, kilopond) = 9.806 65 N (deprecated but persistent)
  • 1 kip = 1000 lbf = 4448.22 N
  • 1 dyne (CGS) = 10⁻⁵ N = 10 µN
  • 1 poundal (pdl) = 0.138 255 N (force giving 1 lb mass 1 ft/s²; absolute FPS unit)
  • 1 ozf = 0.278 014 N
  • 1 tonf (UK long, force of gravity on long ton) = 9964.02 N

10. Pressure

  • 1 Pa = 1 N/m² (very small; atmospheric is ~10⁵ Pa)
  • 1 kPa = 10³ Pa = 0.145 038 psi
  • 1 MPa = 10⁶ Pa = 145.038 psi = 10 bar = 9.8692 atm
  • 1 GPa = 10⁹ Pa = 145 038 psi (engineering modulus scale)
  • 1 bar = 10⁵ Pa = 100 kPa = 14.5038 psi (legacy oceanography & meteorology)
  • 1 atm (standard atmosphere) = 101 325 Pa (exact) = 14.6959 psi = 1.013 25 bar = 760 Torr
  • 1 mbar = 100 Pa = 1 hPa (weather charts use hPa)
  • 1 psi = 6894.757 Pa
  • 1 ksi = 1000 psi = 6.894 757 MPa (steel strength scale)
  • 1 mmHg ≈ 1 Torr = 133.3224 Pa (medical BP, vacuum)
  • 1 inHg (at 0 °C) = 3386.389 Pa (US barometers, manifold vacuum)
  • 1 mmH₂O (4 °C) = 9.806 65 Pa
  • 1 inH₂O (60 °F) = 248.84 Pa; (4 °C) = 249.089 Pa (HVAC manometers)
  • 1 cmH₂O = 98.0665 Pa (ventilator pressure)
  • Vacuum: 1 Pa = 7.500 62 × 10⁻³ Torr; 1 Torr = 1.333 mbar; ultra-high vacuum < 10⁻⁷ Pa.

11. Energy

  • 1 J = 1 N·m = 1 W·s = 1 C·V = 1 Pa·m³
  • 1 cal (thermochemical) = 4.184 J (exact, defined)
  • 1 cal (IT, international steam table) = 4.1868 J
  • 1 kcal = 4.184 kJ (= 1 food Calorie, capital-C “Cal”)
  • 1 BTU (IT) = 1055.056 J; 1 BTU (thermochemical) = 1054.350 J
  • 1 ft·lbf = 1.355 818 J
  • 1 erg (CGS) = 10⁻⁷ J
  • 1 eV = 1.602 176 634 × 10⁻¹⁹ J (exact post-2019)
  • 1 Wh = 3600 J
  • 1 kWh = 3.6 MJ = 3412.14 BTU
  • 1 MWh = 3.6 GJ
  • 1 therm (US) = 100 000 BTU = 105.506 MJ
  • 1 quad = 10¹⁵ BTU = 1.055 EJ (US national energy budget scale)
  • 1 toe (tonne of oil equivalent, IEA) = 41.868 GJ

12. Power

  • 1 W = 1 J/s = 1 N·m/s
  • 1 hp (mechanical / imperial, “horsepower”) = 550 ft·lbf/s = 745.6999 W
  • 1 hp (metric, PS, ch, pk) = 75 kgf·m/s = 735.4988 W
  • 1 hp (electrical) = 746 W (NEMA motor nameplate convention)
  • 1 hp (boiler) = 33 475 BTU/h = 9809.5 W
  • 1 BTU/h = 0.293 071 W
  • 1 BTU/s = 1055.06 W
  • 1 ton (refrigeration, US) = 12 000 BTU/h = 3516.853 W (= rate to freeze 1 short ton of water in 24 h)
  • 1 erg/s = 10⁻⁷ W
  • 1 ft·lbf/s = 1.355 818 W
  • 1 cal/s = 4.184 W

13. Temperature

  • T(K) = T(°C) + 273.15
  • T(°C) = T(K) − 273.15 = [T(°F) − 32] × 5/9
  • T(°F) = T(°C) × 9/5 + 32 = T(K) × 9/5 − 459.67
  • T(°R, Rankine) = T(°F) + 459.67 = T(K) × 9/5

Temperature difference:

  • ΔT(K) = ΔT(°C); ΔT(°R) = ΔT(°F); ΔT(°F) = ΔT(°C) × 9/5 = ΔT(K) × 9/5

Fixed reference points (ITS-90):

  • 0 K = absolute zero = −273.15 °C = −459.67 °F
  • triple point of water = 273.16 K = 0.01 °C
  • ice point (1 atm) = 273.15 K = 0 °C = 32 °F
  • steam point (1 atm) = 373.15 K = 100 °C = 212 °F
  • Réaumur (legacy, °Ré): 0 °Ré ice, 80 °Ré steam; T(°Ré) = T(°C) × 4/5

14. Velocity, acceleration, flow

Velocity:

  • 1 m/s = 3.2808 ft/s = 2.2369 mph = 1.9438 knots = 3.6 km/h
  • 1 mph = 0.447 04 m/s = 1.4667 ft/s = 1.6093 km/h
  • 1 knot (nautical mph) = 0.514 444 m/s = 1.852 km/h (exact)
  • 1 km/h = 0.277 778 m/s

Acceleration:

  • 1 g_n (standard gravity) = 9.806 65 m/s² (exact, defined)
  • 1 g_n = 32.174 05 ft/s²
  • 1 Gal (CGS) = 1 cm/s² = 10⁻² m/s² (geodesy, gravimetry)

Volumetric flow:

  • 1 m³/s = 35.3147 ft³/s (cfs) = 15 850.3 US gpm = 86 400 m³/day
  • 1 US gpm = 6.309 × 10⁻⁵ m³/s = 0.063 09 L/s
  • 1 cfm (ft³/min) = 4.7195 × 10⁻⁴ m³/s = 28.3168 L/min = 1.699 m³/h
  • 1 L/min = 1.6667 × 10⁻⁵ m³/s

Mass flow:

  • 1 kg/s = 7936.6 lb/h = 132.28 lb/min
  • 1 lb/h = 0.000 126 kg/s

Standardized gas flow (referenced to 0 °C, 101.325 kPa):

  • 1 sccm = 1 std cm³/min ≈ 1.667 × 10⁻⁸ m³/s (vol at STP)
  • 1 slpm = 1 std L/min ≈ 1.667 × 10⁻⁵ m³/s
  • 1 scfm = 1 std ft³/min ≈ 4.72 × 10⁻⁴ m³/s
  • Note: “standard” reference state varies by industry — DIN 1343 (0 °C, 1.013 25 bar), ISO 13443 (15 °C, 101.325 kPa), API/AGA (60 °F, 14.696 psia). Always declare.

15. Torque / moment

  • 1 N·m = 0.737 562 lbf·ft = 8.850 75 lbf·in = 10.197 16 kgf·cm
  • 1 lbf·ft = 1.355 818 N·m
  • 1 lbf·in = 0.112 985 N·m
  • 1 kgf·m = 9.806 65 N·m
  • 1 oz·in (mini servo motors) = 7.0616 mN·m
  • 1 dyne·cm (CGS) = 10⁻⁷ N·m

(N·m and J are dimensionally identical but represent distinct quantities — torque is a vector, energy a scalar; never use J for torque.)

16. Viscosity

Dynamic (absolute) viscosity µ:

  • 1 Pa·s = 1 N·s/m² = 1 kg/(m·s) = 10 P (poise) = 1000 cP (centipoise)
  • 1 cP = 1 mPa·s
  • 1 lbf·s/ft² = 47.880 Pa·s
  • Reference: water at 20 °C = 1.002 cP; air at 20 °C = 0.0181 cP; SAE 30 motor oil at 100 °C ≈ 10 cP.

Kinematic viscosity ν = µ/ρ:

  • 1 m²/s = 10⁴ St (stokes) = 10⁶ cSt (centistokes)
  • 1 cSt = 1 mm²/s = 10⁻⁶ m²/s
  • 1 ft²/s = 0.092 903 m²/s = 92 903 cSt

SAE J300 (engine oil winter / summer grades) and ISO VG (industrial, ν at 40 °C) are both expressed in cSt; ISO VG number ≡ ν in cSt at 40 °C.

17. Electrical and magnetic

  • 1 A·h = 3600 C (battery capacity)
  • 1 mA·h = 3.6 C (consumer cell ratings)
  • 1 kW·h = 3.6 MJ (utility billing)
  • ε₀ (vacuum permittivity) = 8.854 187 8128 × 10⁻¹² F/m (measured post-2019)
  • µ₀ (vacuum permeability) = 1.256 637 062 × 10⁻⁶ H/m ≈ 4π × 10⁻⁷ H/m (was exact pre-2019)
  • 1 V/m (field strength), 1 V/µm = 10⁶ V/m (dielectric breakdown)
  • mho (older usage) = S = Ω⁻¹

Magnetic (legacy CGS units still used in MRI, magnetics design):

  • 1 Tesla (T) = 10⁴ Gauss (G)
  • 1 G = 10⁻⁴ T = 100 µT
  • 1 A/m = 4π × 10⁻³ Oersted (Oe); 1 Oe = 79.5775 A/m
  • 1 Maxwell (Mx) = 10⁻⁸ Wb (magnetic flux, CGS)
  • Earth’s surface field ≈ 25–65 µT (0.25–0.65 G).

18. Radiation and dose

Absorbed dose (energy deposited per unit mass):

  • 1 Gy (gray) = 1 J/kg
  • 1 rad = 0.01 Gy = 10 mGy

Equivalent / effective dose (with radiation weighting factor):

  • 1 Sv (sievert) = 1 J/kg × Q (Q = 1 for X/γ/β; 20 for α; 5–20 for neutrons)
  • 1 rem = 0.01 Sv = 10 mSv

Activity (decay rate):

  • 1 Bq (becquerel) = 1 decay/s
  • 1 Ci (curie) = 3.7 × 10¹⁰ Bq (exact, ≈ activity of 1 g ²²⁶Ra)

Exposure (air ionization, X/γ):

  • 1 R (röntgen) ≈ 2.58 × 10⁻⁴ C/kg (air)

Annual background dose typical: 2–3 mSv (terrestrial + cosmic + radon).

19. Photometry and optics

Photometric quantities are weighted by the V(λ) photopic luminous-efficiency function (peak 555 nm).

  • 1 lm/m² = 1 lux (lx), illuminance
  • 1 footcandle (fc) = 1 lm/ft² = 10.7639 lux
  • 1 nit = 1 cd/m² (luminance, e.g., display brightness)
  • 1 stilb (sb, CGS) = 1 cd/cm² = 10⁴ nits
  • 1 foot-lambert (fL) = (1/π) cd/ft² = 3.4263 cd/m²
  • 1 lambert (CGS) = (1/π) cd/cm² × 10⁴

Maximum photopic luminous efficacy: K_cd = 683 lm/W at 540 THz (555 nm). Scotopic peak: 1700 lm/W at 507 nm.

Typical illuminance:

  • moonlight: 0.05–0.3 lx
  • street lighting: 5–30 lx
  • office: 300–500 lx
  • task work: 750–1500 lx
  • overcast daylight: 1000–10 000 lx
  • direct sunlight: 30 000–100 000 lx

20. Wood, lumber, building

  • 1 board-foot (bf) = 144 in³ = 2360 cm³ = 2.36 × 10⁻³ m³ (1 ft × 1 ft × 1 in)
  • Nominal vs actual (US softwood, dried, surfaced S4S, per US PS 20):
    • 2 × 4 → 1.5 × 3.5 in → 38 × 89 mm
    • 2 × 6 → 1.5 × 5.5 in → 38 × 140 mm
    • 2 × 8 → 1.5 × 7.25 in → 38 × 184 mm
    • 2 × 10 → 1.5 × 9.25 in → 38 × 235 mm
    • 4 × 4 → 3.5 × 3.5 in → 89 × 89 mm
  • 1 cord (firewood, stacked) = 128 ft³ = 4 × 4 × 8 ft = 3.6246 m³
  • 1 cord-foot (face cord) = 16 ft³ ≈ 0.453 m³
  • 1 square (roofing) = 100 ft² = 9.290 m²

21. Significant figures and rounding

  • IEEE 754 binary64 (double): ~15–17 significant decimal digits.
  • Half-even rounding (banker’s rounding, IEEE 754 default): ties round to nearest even digit — eliminates systematic bias in large datasets. Half-up (commercial / school) always rounds 0.5 up.
  • Engineering notation: mantissa × 10^(3n) — aligns with SI prefixes (kilo, mega, …). Scientific notation: mantissa × 10^n with 1 ≤ |mantissa| < 10.
  • Rule of thumb: a result is no more precise than the least precise input; sum/difference governed by absolute precision (decimal places), product/quotient by relative precision (sig figs).
  • NIST recommends carrying ≥ 2 guard digits during calculation, rounding only the final answer.

22. Dimensional analysis

The Buckingham π theorem: a physical relation among n variables in k independent dimensions reduces to a relation among (n − k) dimensionless π-groups. Powerful for collapsing experiment design and scaling.

Common dimensionless groups in engineering:

  • Reynolds Re = ρVD/µ — inertial/viscous, fluid mechanics
  • Mach Ma = V/a — compressibility
  • Prandtl Pr = ν/α = c_p µ/k — momentum/thermal diffusivity
  • Nusselt Nu = hL/k — convective/conductive heat transfer
  • Grashof Gr = gβΔT L³/ν² — buoyancy/viscous (natural convection)
  • Rayleigh Ra = Gr·Pr
  • Biot Bi = hL/k_solid — surface/interior resistance
  • Fourier Fo = αt/L² — dimensionless time, conduction
  • Weber We = ρV²L/σ — inertial/surface tension
  • Froude Fr = V/√(gL) — inertial/gravity, free-surface flow
  • Strouhal St = fL/V — vortex shedding
  • Knudsen Kn = λ/L — molecular mean free path / characteristic length; rarefied gas
  • Schmidt Sc = ν/D_AB — momentum/mass diffusivity
  • Sherwood Sh = hₘL/D_AB — convective/diffusive mass transfer
  • Damköhler Da = reaction rate / transport rate

Worked example — turbomachine: dimensional analysis shows head H = f(Q, N, D, ρ, gµ) collapses to ψ = gH/(N²D²) as a function of φ = Q/(ND³) and Re — basis of pump/fan affinity laws.

23. Cross-references

24. Citations

  • BIPM, The International System of Units (SI Brochure), 9th ed., 2019 (rev. 2022 with new prefixes). https://www.bipm.org/en/publications/si-brochure
  • NIST, Special Publication 811 — Guide for the Use of the International System of Units (SI), 2008 ed. (Thompson & Taylor).
  • NIST, Special Publication 330 — The International System of Units (SI) (2019 US edition).
  • CIPM, Mise en pratique for each base unit (2019).
  • ASTM E380 / IEEE/ASTM SI 10, Standard for Use of the International System of Units (SI): The Modern Metric System.
  • ISO 80000 series — Quantities and Units (parts 1–14, replacing ISO 31).
  • NIST CODATA Recommended Values of the Fundamental Physical Constants (2018 adjustment, with 2019 redefinition impact).
  • 26th CGPM Resolution 1 (2018) — adoption of the revised SI, effective 20 May 2019.
  • 27th CGPM Resolution 3 (2022) — adoption of prefixes ronna, quetta, ronto, quecto.

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