Kitstead Labs

General

Engineering Unit Converter

Convert the units that show up in plating, deposition, vacuum and contamination work: thickness, ratios, pressure, current density, rates and gas flow. Factors come from NIST SP 811; the tool adds no data of its own.

01Inputs

Only units in the same group as “From” can be chosen.

02Result

03Method

AHow it is calculated
  1. Groups. Units are converted only within one group: length / thickness, ratio, pressure, current density, deposition / etch rate, and gas flow. A unit in one group has no fixed relation to a unit in another.
  2. Through the base unit. Each unit has one factor to its group's base unit (m, 1, Pa, A/m², m/s or sccm). The value is multiplied by the factor of the “From” unit and divided by the factor of the “To” unit.
  3. Sources. Factors come from NIST SP 811 (2008), Appendix B.8, and the SI prefixes. For example 1 inch = 0.0254 m and 1 standard atmosphere = 101 325 Pa are exact by definition; 1 Torr is defined as 1/760 atm.
  4. Exact factors, rounded display. Every factor here is exact by definition, including 1 Torr = 101 325/760 Pa. What differs is the decimal: 1 mil = 25.4 µm terminates, while 1 Torr = 133.322 368… Pa does not and is rounded for display. The result line says which applies to the chosen pair, which can terminate even when each unit's own factor does not: 1 A/dm² = 9.290 304 A/ft² exactly, because the foot is exactly 0.3048 m.
  5. Display. Results show up to 10 significant figures with trailing zeros removed, and switch to powers of ten below 10⁻⁶ or from 10¹². A value too large to represent shows “Value out of range”.
BScope and limitations
  • Gas flow at standard conditions only. sccm, slm and mL/min are converted among themselves on the assumption that all three are stated at the same standard conditions. Industries define those conditions differently (0 °C or 20 °C at 1 atm), and this tool does not convert between temperatures or to molar flow.
  • Ratios are numbers. %, ppm and ppb are plain ratios (10⁻², 10⁻⁶, 10⁻⁹). Whether a ppm is by mass, by volume or by mole is not part of the unit; state it beside the number. NIST SP 811 (7.10.3) recommends writing the ratio explicitly instead of using ppm and ppb.
  • ppb is short scale. 1 ppb = 10⁻⁹. Some older texts use a long-scale billion (10¹²).
  • Rates are averages. µm/min, nm/s, Å/s and µm/h convert an average rate; they say nothing about how the rate changes during a process.
CCommon mistakes
  • Reading mil as millimeter. A mil is one thousandth of an inch, 25.4 µm, about 1/40 of a millimeter.
  • Treating mL/min as sccm at process conditions. A volumetric flow measured at the actual gas temperature and pressure is not an sccm value; it equals sccm only once it is stated at the standard conditions.
  • Mixing up Torr and mTorr. Vacuum gauges often read in mTorr; 100 mTorr is 0.1 Torr, about 13.3 Pa.
  • Inverting the ASD–ASF factor. 1 A/dm² is about 9.29 A/ft², and 1 A/ft² is about 0.108 A/dm². Multiplying A/dm² by 10.76, the square-foot-to-square-meter factor, instead of 9.29 is a common slip.
  • Comparing ppm values of different kinds. A ppm by mass and a ppm by volume of the same contaminant are not the same amount.

Further reading

Tracking thickness or rate data over time? SPC & Capability Analyzer for Excel