Unit Converter — Companion Article

1. What this tool does

The page converts a number between units of one quantity. The quantities are length, area, volume, mass, temperature, pressure, flow, density, force, energy, power, velocity and torque.

The arithmetic runs in the browser. The factors are in one data file. Each factor names its source. Factors that are exact by definition are marked. Temperature is not a factor. It uses the offset formulas for Celsius, Fahrenheit, kelvin and rankine.

Flow has two separate lists. Volumetric flow uses m3/h, m3/s, L/s, L/min, US gpm, imperial gpm, ft3/min and bbl/day. Mass flow uses kg/h and lb/h. The page does not convert one list into the other.

Pressure labels bar(g), bar(a), psi(g) and psi(a). Unlabeled bar and psi are absolute, the same scales as bar(a) and psi(a). A gauge conversion adds or subtracts the standard atmosphere and says so on the page. That reference is 101.325 kPa, which is 101325 Pa.

The page does not call the Engineering API. It does not look up pipe, flange or valve records.

2. When to use it

Use it when a designer needs a stated factor between units of one of those quantities. It is not a pipe-size tool. It does not size, rate or select a component.

3. Inputs

1. Choose the quantity. The heading of the active tab is that quantity.
2. On the flow tab, the page keeps volumetric flow and mass flow as separate lists. A conversion stays inside the list that is open.
3. Type the value. Choose From and To.
4. Full precision is a choice. Otherwise the page shows 6 significant figures.

The page does not ask for a density, a local barometer, a pipe size, or a catalogue record.

4. How it works

The running tool is the calculation. This section describes the method already in version 1.0.0. It does not add a second factor table.

For a quantity that uses a factor, the data file holds the factor into the SI base for that quantity. Each factor names its source. A factor marked exact is exact by definition, or an exact product of defining values. Where NIST Special Publication 811, Appendix B, prints a rounded factor, the data file stores the exact product and says so.

Temperature does not use that factor path. The page uses the offset formulas for Celsius, Fahrenheit, kelvin and rankine. The identities already recorded for those formulas are in section 7.

Pressure converts on the absolute scale. Unlabeled bar and unlabeled psi are absolute. A gauge unit, bar(g) or psi(g), adds or subtracts one standard atmosphere, 101325 Pa, shown on the page as 101.325 kPa. A conversion between two absolute units does not add it.

Volumetric flow and mass flow stay on separate lists. The page does not cross from one list to the other.

The petroleum barrel on the flow tab is 42 US gallons. The day is 86400 seconds.

5. Understanding the result

The large number is the converted value in the To unit. It is shown at 6 significant figures unless full precision is on. Full precision shows the calculated value to the digits the page can hold.

On the pressure tab, the note states the atmospheric reference, 101.325 kPa. If the conversion uses a gauge unit, the note also says that this result adds or subtracts that reference. A conversion between two absolute units does not add it.

Under the result, the page quotes the source of the From unit and the source of the To unit.

Swap units exchanges the two units and puts the converted number in the value box. Copy result copies the displayed number and unit.

6. Engineering considerations

Gauge and absolute differ by one standard atmosphere. The page does not ask for a local barometer. A site that is not at that atmosphere should not treat a gauge conversion as the local absolute pressure.

Unlabeled bar and unlabeled psi are absolute. A drawing that writes “bar” for barg will be misread if those labels are used as absolute.

Conventional mmHg and conventional inH2O are the defined metrology columns named on the page. They are not a measured mercury or water column at some other temperature.

Mass flow and volumetric flow stay apart. The page does not assume a density.

The result is a unit conversion. It is not a pipe size, a pressure rating, or a component selection. The NPS / DN / OD link on the page is a separate cross-reference. It is not a conversion performed by this tool.

7. Example

These are the definitions the page uses, and the acceptance checks in the 1.0.0 read-me. They are not a piping problem. This article does not add a piping conversion. The checks were not re-run on a live tool for this remap.

Definitions already recorded for version 1.0.0:

• 1 in = 0.0254 m exactly.
• 1 ft = 0.3048 m exactly.
• 1 lb = 0.45359237 kg exactly.
• 1 L = 0.001 m3 exactly.
• 1 US gal = 231 in3 = 0.003785411784 m3 exactly.
• 1 imperial gal = 4.54609 L exactly.
• 0 C = 32 F = 273.15 K.
• 100 C = 212 F.
• -40 C = -40 F.
• 1 bar = 100000 Pa exactly.
• 1 atm = 101325 Pa = 101.325 kPa exactly.
• 0 bar(g) = 1.01325 bar(a), because 101325 / 100000 = 1.01325.
• 1 kgf/cm2 = 98066.5 Pa exactly.
• Conventional millimetre of mercury = 133.322387415 Pa exactly. NIST SP 811 prints this factor rounded.
• Conventional inch of water = 249.08891 Pa exactly. NIST SP 811 prints this factor rounded.
• 1 lbf = 4.4482216152605 N exactly.
• 1 mechanical horsepower = 550 ft lbf/s = 745.69987158227022 W exactly.
• International Table Btu = 1055.05585262 J exactly.

Acceptance checks already written for the page:

• 1 in returns 25.4 mm.
• 100 C returns 212 F. 0 C returns 273.15 K.
• 0 bar(g) returns 1.01325 bar(a), and the note shows 101.325 kPa.
• 1 psi returns 6894.76 Pa at 6 significant figures.
• Volumetric flow does not offer kg/h. Mass flow does not offer m3/h.

8. Standards/references (licensed vs interim)

SI Brochure, for the SI prefixes, the litre, and the Celsius–kelvin offset of 273.15.

NIST Special Publication 811, Appendix B, for the yard and pound identities, the standard atmosphere, the bar, standard gravity 9.80665 m/s2, and the printed conversion tables. Where Appendix B prints a rounded factor, the data file stores the exact product of the defining values and says so.

The petroleum barrel on the flow tab is 42 US gallons. The day is 86400 seconds.

This draft does not class those sources as licensed standards data, and it does not class them as interim owner-authorised data. The interim pattern in the owner decisions log is ASME B36.10-2022 Table 2-1. This tool does not use that table. Owner engineering review confirms the source classification before publish.

The page does not call the Engineering API. It does not look up pipe, flange or valve records.

9. Limitations/disclaimer

The disclaimer already on the tool: this page converts units. It does not read the Engineering API and it does not size or rate piping. Unlabeled bar and psi are absolute. Gauge conversions use the standard atmosphere, 101.325 kPa.

• The displayed short result is rounded to 6 significant figures. Full precision is still a binary floating-point evaluation of an exact decimal or ratio, so the last digit of a long result can differ from an exact fraction. The reference checks compare the engine with the exact values above.
• Gauge and absolute differ by one standard atmosphere. The page does not ask for a local barometer. A site that is not at that atmosphere should not treat a gauge conversion as the local absolute pressure.
• Conventional mmHg and conventional inH2O are the defined metrology columns named on the page. They are not a measured mercury or water column at some other temperature.
• Unlabeled bar and unlabeled psi are absolute. A drawing that writes “bar” for barg will be misread if those labels are used as absolute.
• Mass flow and volumetric flow stay apart. The page does not assume a density.
• The page does not size, rate or select a component.

A member check is not an engineering fact. The note is under Repository notes. It is not one of the ten sections.

10. Use the tool

Calculate now: Unit converter

Shortcode:

. Version 1.0.0. The page is recorded as live. Re-check this article when the tool version changes.

How this calculation works: companion path TBD.

That return link is not on the tool page. This draft does not add it to the plugin. The public article path is still TBD because this file is not published.

The article stays public if the tool is later restricted. A visitor with no entitlement for the tool sees a lock message on the tool, not a bare “Access denied”. The copy for that message is in the Companion Article standard. This draft does not place that lock on version 1.0.0.

Related tools

The page links to the NPS / DN / OD cross-reference. The path is a plugin setting. Until it is changed, the link is /tools-training/nps-dn-od-cross-reference/.

That cross-reference is the related tool already named on this page. This section does not add another calculation.