About Engineering Unit Converter — Pressure, Flow, Viscosity, Length & More
The engineering unit converter is the hub for the quantities that do not have a dedicated converter on this site: dynamic viscosity (pascal-seconds, centipoise, poise, and the US customary lbf·s/ft²), kinematic viscosity (m²/s, centistokes, stokes, ft²/s), and the geometric trio of length, area, and volume from millimeters and square inches up to miles, acres, hectares, and cubic yards. Pick the quantity, and the unit selects switch to that quantity's set — with the from/to units reset to sensible defaults so a stale unit from another quantity can never leak into the conversion.
Every set converts through its SI base unit with NIST SP 811 Appendix B factors. The international inch-pound length family is exact by definition (1 in = 25.4 mm, so 1 ft = 0.3048 m and 1 mi = 1,609.344 m), as are the metric viscosity relations (1 cP = 1 mPa·s, 1 cSt = 1 mm²/s); the acre carries NIST's published US-survey-based value of 4,046.873 m². For pressure, flow, temperature, torque, power, and energy, use the dedicated converters — each has its own chart and unit notes.
How It Works
- Pick the quantity first — dynamic viscosity, kinematic viscosity, length, area, or volume. The unit selects repopulate with that quantity's units and reset to its most common conversion (100 cP → Pa·s, 1 acre → ft², 10 US gal → L, ...).
- Enter the value, choose the from and to units, and read the headline conversion plus the all-units table below it. Every conversion is value × (base units per from-unit) ÷ (base units per to-unit) in full double precision.
- The two viscosities are different quantities and cannot be converted into each other by units alone: kinematic viscosity is dynamic viscosity divided by density (ν = μ/ρ). Oil datasheets usually quote cSt (kinematic); process calculations often need cP (dynamic) — the bridge is the fluid's density, not a factor.
- Displayed values are rounded to 6 significant digits. Round-trips return your original number, and the exact-by-definition factors (the inch family, hectare, liter) introduce no rounding at all.
Worked Example
A site plan lists a 1-acre parcel and the drainage calculation wants square feet and square meters. Through the base unit: 1 acre = 4,046.873 m² (NIST's US-survey-based factor), and 4,046.873 ÷ 0.09290304 m² per ft² = 43,560.2 ft² — the statutory 43,560 ft² definition reproduced to within the survey-vs-international-foot hair (about 0.2 ft² in an acre). The same parcel is 0.404687 hectares, the chart's "1 acre" row.
Acres to square feet conversion chart (with m² and hectares)
Common parcel sizes converted with the NIST SP 811 factors (1 acre = 4,046.873 m², US survey based; 1 ft² = 0.09290304 m² exact), shown to 6 significant digits — exactly what the converter outputs for the same inputs. The familiar 43,560 ft² per acre appears with a ~0.2 ft² survey-foot hair.
| Area | ft² | m² | hectares |
|---|---|---|---|
| 0.25 acre (suburban lot) | 10,890 | 1,011.72 | 0.101172 |
| 0.5 acre (large lot) | 21,780.1 | 2,023.44 | 0.202344 |
| 1 acre | 43,560.2 | 4,046.87 | 0.404687 |
| 2 acres | 87,120.4 | 8,093.75 | 0.809375 |
| 5 acres (hobby farm) | 217,801 | 20,234.4 | 2.02344 |
| 10 acres | 435,602 | 40,468.7 | 4.04687 |
Formulas
- Conversion through the quantity's SI base unit
x = value × f_from ÷ f_to- Viscosity factors
cP 10⁻³ Pa·s · poise 0.1 Pa·s · lbf·s/ft² 47.88026 Pa·s · cSt 10⁻⁶ m²/s · stokes 10⁻⁴ m²/s · ft²/s 0.09290304 m²/s- Length, area & volume factors
in 25.4 mm · ft 0.3048 m · yd 0.9144 m · mi 1,609.344 m · in² 6.4516 cm² · ft² 0.09290304 m² · acre 4,046.873 m² · ha 10⁴ m² · in³ 16.387064 cm³ · ft³ 0.02831685 m³ · US gal 3.785412 L · yd³ 0.7645549 m³
Standards & References
- NIST SP 811, Guide for the Use of the International System of Units, Appendix B — conversion factors for viscosity (lbf·s/ft² 4.788026×10¹ Pa·s), area (acre 4.046873×10³ m²), and volume (US gal 3.785412×10⁻³ m³; ft³ 2.831685×10⁻² m³; yd³ 7.645549×10⁻¹ m³)
- Exact definitions: 1 in = 25.4 mm (1959 international yard and pound agreement); 1 cP = 1 mPa·s; 1 cSt = 1 mm²/s; 1 ft²/s = 0.09290304 m²/s; 1 in³ = 16.387064 cm³; 1 ha = 10⁴ m²; 1 L = 10⁻³ m³
- Dedicated converters on this site handle pressure, flow rate, temperature, torque, power, and energy
Frequently Asked Questions
What is the difference between dynamic and kinematic viscosity?
Dynamic viscosity μ (Pa·s, cP) measures a fluid's resistance to shear; kinematic viscosity ν (m²/s, cSt) is μ divided by the density: ν = μ/ρ. They are different physical quantities, which is why the tool keeps them as separate quantity groups — converting cSt to cP is not a unit conversion but a multiplication by the fluid's density in g/cm³ (for water at 20 °C, ≈1, which is why 1 cSt ≈ 1 cP there and nowhere else).
How many square feet are in an acre?
By definition 43,560 ft² (a chain by a furlong, 66 × 660 survey feet). Converting through NIST's metric factor — 4,046.873 m² per acre ÷ 0.09290304 m² per international ft² — gives 43,560.2 ft², because the acre is defined on the US survey foot, which is 2 ppm longer than the international foot. For land arithmetic either number is fine; the chart shows the converter's exact output.
Why does switching the quantity reset my unit selections?
Because unit keys only mean something inside their own set — carrying "cP" into the length set would be nonsense, and silently keeping a stale selection is how converters produce garbage numbers. On every quantity switch the tool resets from/to to that quantity's most common pair (acre → ft², cP → Pa·s, US gal → L), and the calculation layer independently rejects any unit key that is not in the active set.
Which gallon and which mile does this tool use?
The US liquid gallon (3.785412 L per NIST SP 811 — the imperial gallon is 4.546 L, about 20% larger) and the international statute mile (1,609.344 m exactly, from the 1959 definition of the foot). Nautical miles (1,852 m exactly) are a different unit used for navigation and are not in the set.
Where are pressure, temperature, and the other quantities?
Each has a dedicated converter with its own chart and unit notes: pressure (psi, bar, kPa, atm), flow rate (CFM, GPM, L/s), temperature (°C, °F, K, °R — affine, with an absolute-zero guard), torque (Nm, ft-lb), power (kW, HP, BTU/h, tons), and energy (kWh, BTU, therms). This hub deliberately covers only the quantities without a dedicated tool, so every conversion on the site lives in exactly one place.