# For length in aircraft design, and in weight and balance manuals, what measurement unit does Airbus use?

What length measurement unit does Airbus use for aircraft design and in their weight and balance manuals? Meters or centimeters?

Possibly they use both like Boeing does for, say, feet plus inches for overall length and wingspan but just inches for a position along the longitudinal axis for crew, pax, and cargo locations? For example 1821.0 inches for the lower hold aftmost ULD position on a 747.

• Are you asking about something specific like station numbers (for things like ribs and fuselage frames)? Commented Apr 17, 2019 at 8:47
• @Hobbes I'm interested in the balance arms along the longitudinal axis for crew, pax, fuel and cargo locations. Station numbers typically reflect the balance arms in the first model designs but then may not when when the original design is lengthened. Commented Apr 17, 2019 at 17:00
• Terry, do you consider meter and centimeter as two distinct units? In my view they are not. They only have an impact on the presentation of significant digits.
– bogl
Commented Apr 18, 2019 at 9:26
• @bogl Even if I might like to consider them as different gradations of the same unit, practical usage forces me to treat them as distinct units. If I am presented with a number delineating the position of a ULD along the longitudinal axis of an airplane, the code I write to calculate the c.g. has to take into account whether that number is in meters or centimeters. Commented Apr 18, 2019 at 15:14

Structures are soft metric. Airbus uses inch hardware so some measurements make sense in inches but are drawn with an ugly mm number. The coordinate system is in metric.

The rest of the aircraft is hard metric. For example, MTOW and fuel capacity is in a nice number of kg.

Documentation and instrumentation is localized according to the operator. Mass, as in fuel, can be switched between kg and lbs on ECAM, and all the manuals and W&B will follow.

There's a few units that aren't localized, most notably pressure is always in PSI and engine oil is always given in quarts (probably since it comes in quart cans).

In the FCOM for the A320 the dimensions are listed in both decimal meters and in feet+inches.

source: A320 FCOM

• I also notice that in this particular FCOM they use the point for a decimal, but in a few places above they apparently missed changing them from the comma decimal more common in France Commented Apr 17, 2019 at 2:51
• At least they didn't specify three decimal digits; a tail width of 12,450m or 11,510m between the engine centers might have been "obviously wrong", but could still lead to a bit of headscratching in less obvious situations.
– user
Commented Apr 17, 2019 at 8:31

The (few) design drawings I‘ve seen were in millimeters; however I can’t confirm whether that’s the uniform standard.

I think the operations manuals are available in metric and imperial units for the operator to choose.