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This page is devoted to *frequently asked questions* (FAQ) related to units.
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h2. In which unit is mass entered?

*Answer:* [Mass|kb:Mass] must be given in consistent mass units (W/g). Force, length, and temperature are primary units. Mass is then derived from these units secondarily. Accordingly, notable points include the following:

# Ton represents ton-force (tonf) when the Ton, m, C unit set is chosen.
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# A mass of 1.0 tonm, also known as a tonne or metric ton, is given as 1000 kg. In a standard gravity field, the weight of 1.0 tonm produces 1.0 tonf, or a ton-force, given as 9810 Newtons (N).
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# Because mass must be entered in consistent units (W/g), and not as a force, 1.0 tonf would be entered as W/g = 1 tonf / (9.81 m/s{^}2{^}2^) = 0.102 tonf * s{^}2{^}2^/m.

Additional information may be found in the [Mass units|kb:Mass units] article and in the {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} [_Analysis Reference Manual_|doc:CSI Analysis Reference Manual] (Joints and Degrees of Freedom > Masses, page 39).

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*Related Incident:*
* {incident:no=30627|comment=Mass input questions}
The following explanation is provided in Incident 30267: In SAP2000, the basic units are Force (lb, kip, N, kN, etc.), Length (ft, in, m, mm, etc.), Time (second), and Temperature (F, C). Mass is a derived unit and SAP2000 does not use lb or kip for mass units, they are only used for force units. Weight has units of F, where F is force. CONSISTENT mass units are given by F/(L/T^2), where L is length, T is time, and the mass units are simply force divided by UNIT acceleration.
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