88 values, each with its units, its uncertainty, and where it came from.
All 351 constants →
mAbsolute roughness ε of new uncoated cast iron pipe, about 0.26 mm — five times rougher than steel, and far worse when tuberculated.
mAbsolute roughness ε of new commercial steel or wrought-iron pipe, 0.046 mm (0.00015 ft) — the Moody-chart default.
mAbsolute roughness ε of drawn copper tube, glass and smooth plastic pipe, about 0.0015 mm — 30 times smoother than steel.
W9809.5 W (33475 BTU/h): the heat rate to evaporate 34.5 lb/h of water at 212 °F, and nothing at all to do with mechanical horsepower.
JThe international-table BTU is exactly 1055.05585262 J, the heat that raises one pound of water by one degree Fahrenheit.
PaIsothermal bulk modulus of liquid water at 20 °C and 1 atm, about 2.18 GPa — a 0.005 % volume change per bar of pressure.
PaTypical specified 28-day cylinder strength of ordinary structural concrete, about 28 MPa (4000 psi), with 20–40 MPa the usual range.
kg/m³Typical density of 6061 aluminium alloy at 20 °C, 2700 kg/m³ or 169 lb/ft³ — about 35 % of steel for the same volume.
kg/m³Density of dry air at 20 °C and 101.325 kPa, 1.204 kg/m³ — the standard-air value behind the 1.08 sensible-heat factor.
kg/m³Density of ordinary hexagonal ice at 0 °C and 1 atm, about 917 kg/m³ — roughly 8 % lighter than the water it freezes from.
kg/m³Density of liquid mercury at 20 °C and 1 atm, 13 534 kg/m³ — 13.5 times water, and the basis of the mmHg pressure unit.
kg/m³Typical density of normal-weight reinforced concrete, 2400 kg/m³ or 150 lb/ft³, including ordinary reinforcing steel content.
kg/m³Representative density of open-ocean seawater at 35 g/kg salinity and 15 °C, about 1025 kg/m³ or 64 lb/ft³ at the surface.
kg/m³Representative density of construction softwood such as spruce-pine-fir or Douglas fir at 12 % moisture, roughly 500 kg/m³.
kg/m³Typical density of carbon and low-alloy structural steel at 20 °C, 7850 kg/m³ or 490 lb/ft³, essentially independent of grade.
Pa·sDynamic viscosity of dry air at 20 °C and 1 atm, 18.1 µPa·s — about 1/55 of water's, though its kinematic viscosity is 15× larger.
Pa·sDynamic viscosity of a typical SAE 30 mineral engine oil at 40 °C, roughly 0.088 Pa·s — about 90 times that of water at 20 °C.
Pa·sDynamic viscosity of pure water at 20 °C and 1 atm, 1.002 mPa·s — the value that made the centipoise a de facto standard.
Ω·mResistivity of pure aluminium at 20 °C, 2.65 × 10⁻⁸ Ω·m; EC-grade 1350 conductor is about 2.83 × 10⁻⁸ Ω·m (61 % IACS).
Ω·mResistivity of plain carbon steel at 20 °C, roughly 1.4–1.8 × 10⁻⁷ Ω·m — about ten times copper's, and composition-sensitive.
Ω·mResistivity of pure annealed copper at 20 °C, 1.678 × 10⁻⁸ Ω·m; the commercial IACS reference is 1.7241 × 10⁻⁸ Ω·m.
—Total hemispherical emissivity of flat black paint near room temperature, about 0.96 — the practical stand-in for a black body.
—Total emissivity of oxidised or mill-scaled carbon steel, about 0.8 — against roughly 0.1 for the same steel polished bright.
—Total hemispherical emissivity of bright polished aluminium near room temperature, about 0.05 — an excellent radiant barrier.
—Representative static friction coefficient for clean dry steel on steel, about 0.6 with a legitimate range of 0.4 to 0.8.
—Representative friction coefficient for oil-lubricated steel on steel in boundary lubrication, about 0.10 (range 0.05–0.15).
—Representative peak friction coefficient for a passenger tyre on dry asphalt, about 0.8 — competition tyres exceed 1.0.
—Representative friction coefficient for a passenger tyre on wet asphalt, about 0.5, falling to 0.3 or below on worn tyres.
—Hazen-Williams roughness coefficient for aged unlined cast iron pipe, typically 100 — new pipe is near 130, badly tuberculated near 60.
—Hazen-Williams roughness coefficient for smooth plastic pipe such as PVC, PE and CPVC, conventionally taken as 150 for design.
—γ = cp/cv = 1.400 for dry air near 20 °C and 1 atm, the exponent in adiabatic compression and in the speed of sound.
—γ ≈ 1.33 for low-pressure steam at 100 °C: a triatomic bent molecule with rotational modes that lower it well below air's 1.40.
KZero degrees Celsius is exactly 273.15 K, the offset that converts every Celsius reading to absolute temperature in gas-law work.
HzNominal 50 Hz AC power frequency used across Europe, Asia, Africa and Oceania, regulated to roughly ±0.05 Hz in normal grid operation.
HzNominal 60 Hz AC power frequency across North America, held within about ±0.05 Hz by grid operators balancing generation against load.
—Manning roughness coefficient for finished concrete channels and pipe, typically 0.013 with a defensible range of 0.011 to 0.016.
J/cal (IT)4.1868 joules per international-table calorie, exact by definition — the conversion Joule spent two decades measuring by hand.
VNominal 230 V RMS single-phase supply under IEC 60038, the harmonised European figure that replaced the old 220 V and 240 V standards.
VNominal 120 V RMS at North American outlets, with ANSI C84.1 allowing roughly 114–126 V at the point of utilisation under normal service.
—Poisson's ratio of wrought aluminium alloys in the elastic range, about 0.33 — slightly higher than steel's 0.30.
—Poisson's ratio of hardened normal-weight concrete under service compression, typically 0.15–0.25 with 0.20 used in design.
—Poisson's ratio of natural and synthetic rubber, about 0.499 — nearly incompressible, the practical limit for isotropic solids.
—Poisson's ratio of carbon and alloy steel in the elastic range, 0.30 — the lateral contraction per unit of axial extension.
—Typical dielectric constant of dry air at 0 °C and one atmosphere — so close to vacuum that most capacitor and antenna work ignores the difference.
PaShear modulus of common wrought aluminium alloys at room temperature, about 26 GPa or 3800 ksi — one third of steel's value.
PaShear (rigidity) modulus of structural steel at room temperature, 77.2 GPa or 11 200 ksi — the value used in torsion and shear.
J/(kg·K)R/M for dry air, 287.0528 J/(kg·K), using the standard-atmosphere molar mass 28.9644 g/mol — the R in p = ρRT for air.
J/(kg·K)R/M for water vapour, 461.523 J/(kg·K), from a molar mass of 18.015268 g/mol — the constant behind psychrometrics and humidity ratio.
—Specific gravity of the mineral solids in most soils, about 2.65 for quartz sands and 2.70–2.75 for clays — remarkably consistent.
J/(kg·K)About 1005 J/(kg·K) at constant pressure for dry air near 300 K and 1 atm; cv is 718 J/(kg·K), and their ratio is γ = 1.40.
J/(kg·K)Specific heat of a 30 % by volume propylene glycol/water mix near 40 °C, about 3850 J/(kg·K) — some 8 % below plain water.
J/(kg·K)Specific heat of plain carbon steel near room temperature, about 486 J/(kg·K) or 0.116 BTU/(lb·°F), rising with temperature.
m/sSpeed of sound in dry air at 20 °C and 1 atm, 343 m/s or 1125 ft/s — set by temperature, essentially not by pressure.
m/sLongitudinal (bulk) wave speed in carbon steel, about 5900 m/s; the thin-bar wave speed √(E/ρ) is lower, near 5100 m/s.
m/sSpeed of sound in fresh water at 20 °C and 1 atm, about 1482 m/s — 4.3 times faster than in air, and rising with temperature.
m/s²The conventional value of free-fall acceleration, exactly 9.806 65 m/s² — a defined reference, not a measurement of your local g.
PaOne standard atmosphere is exactly 101325 Pa, equal to 14.6959 psi, 760 mmHg, 29.921 inHg or 1.01325 bar, by international definition.
1/KTemperature coefficient of resistance for annealed copper referenced to 20 °C, 0.00393 per kelvin — 0.393 % more resistance per degree.
PaMinimum ultimate tensile strength of an SAE Grade 5 bolt up to 1 in diameter, 120 ksi or 827 MPa, with 85 ksi proof strength.
PaMinimum ultimate tensile strength of an SAE Grade 8 bolt, 150 ksi or 1034 MPa, with 130 ksi proof — the high-strength shop fastener.
W/(m·K)Thermal conductivity of dry air at 20 °C and 1 atm, about 0.026 W/(m·K) — the benchmark every insulation is measured against.
W/(m·K)Thermal conductivity of pure aluminium at 25 °C, about 237 W/(m·K); alloy 6061-T6 is markedly lower at roughly 167 W/(m·K).
W/(m·K)Thermal conductivity of plain carbon steel near room temperature, roughly 50 W/(m·K) — about an eighth of copper's value.
W/(m·K)Thermal conductivity of normal-weight structural concrete, roughly 1.4–2.0 W/(m·K) depending on aggregate and moisture content.
W/(m·K)Thermal conductivity of pure annealed copper at 25 °C, about 401 W/(m·K) — the benchmark for practical heat-transfer materials.
W/(m·K)Thermal conductivity of standard fibreglass batt at 24 °C, about 0.040 W/(m·K) — roughly R-3.6 per inch in US units.
W/(m·K)Aged thermal conductivity of rigid polyisocyanurate or XPS board, roughly 0.024–0.029 W/(m·K), about R-5 to R-6 per inch.
W/(m·K)Thermal conductivity of Type 304 austenitic stainless steel at 20 °C, about 16 W/(m·K) — roughly a third of carbon steel's.
W/(m·K)Thermal conductivity of liquid water at 20 °C and 1 atm, about 0.60 W/(m·K) — high for a liquid, still 700× worse than copper.
1/KLinear expansion coefficient of aluminium near room temperature, 23.4 µm/(m·K) or 13 µin/(in·°F) — twice that of steel.
1/KLinear thermal expansion coefficient of carbon steel near room temperature, 11.7 µm/(m·K) or 6.5 µin/(in·°F).
1/KLinear expansion coefficient of normal-weight concrete, roughly 8–12 µm/(m·K) — close enough to steel to make reinforcing work.
1/KLinear expansion coefficient of copper near room temperature, 16.8 µm/(m·K) or 9.3 µin/(in·°F) — 44 % more than steel.
1/KLinear expansion coefficient of rigid PVC pipe, about 54 µm/(m·K) or 3.0 µin/(in·°F) — nearly five times that of steel.
1/KLinear expansion coefficient of Type 304 austenitic stainless steel, 17.3 µm/(m·K) — about 50 % more than carbon steel.
WExactly 12000 BTU/h = 3516.85 W: the cooling rate that melts one short ton of ice in 24 hours, still the unit chillers are sold in.
KThe unique 273.16 K (0.01 °C) at which ice, liquid water and vapour coexist — exact until 2019, now a measured value good to 0.1 mK.
Pa611.657 Pa, about 0.6 % of an atmosphere: the vapour pressure at water's triple point and the floor below which liquid water cannot exist.
N/m³Typical moist bulk unit weight of loose sand, about 15.5 kN/m³ or 99 lbf/ft³; dense sand runs nearer 19.5 kN/m³.
N/m³Typical saturated unit weight of soft normally consolidated clay, about 16 kN/m³ or 102 lbf/ft³, with 14–18 kN/m³ the usual range.
PaSaturation vapour pressure of water at 20 °C, 2339 Pa (0.339 psia) — the absolute pressure at which 20 °C water boils.
PaTypical 0.2 % offset yield strength of 6061-T6 aluminium, 276 MPa or 40 ksi, with an ultimate tensile strength near 310 MPa.
PaSpecified minimum yield strength of ASTM A36 structural steel, 36 ksi or 248 MPa — a floor guaranteed by the mill, not a measurement.
PaSpecified minimum yield strength of ASTM A992 wide-flange steel, 50 ksi or 345 MPa — the default grade for W-shapes since 1998.
PaElastic modulus of 6061 aluminium at room temperature, 68.9 GPa or 10 000 ksi — roughly one third the stiffness of steel.
PaSecant elastic modulus of 28 MPa (4000 psi) normal-weight concrete, about 25 GPa — computed from strength, not measured directly.
PaElastic modulus of carbon and low-alloy structural steel at room temperature, 200 GPa or 29 000 ksi, effectively grade-independent.
PaElastic modulus of annealed Type 304 austenitic stainless steel at 20 °C, about 193 GPa or 28 000 ksi — 3 % below carbon steel.
