Foreword

This British Standard has been prepared by Technical Committee SS/7. It supersedes BS 350‑1:1974 which is withdrawn.

BS 350 was first published in 1930, and has been revised on a number of occasions since. It was split into two parts in 1959, Part 1 dealing with the basis of tables and conversion factors, and Part 2, which first appeared in 1962, giving detailed conversion tables for the more frequently used conversions. In 1967 a Supplement (PD 6203) was issued to Part 2, giving additional detailed tables for SI conversions. BS 350‑2 was withdrawn in 1981 since many of the tables included in it had become inconsistent with the International System of Units (SI) and the increasing use of pocket calculators was considered to have made such tables, which often required interpolation, obsolete. PD 6203 was withdrawn in 1998.

This revision provides a comprehensive list of conversion factors and notes on their use. The units in about fifty quantities of measurement are given, together with such definitions and information on the derivation of conversion factors as are considered necessary for the purpose. However, as it is now the only part of the standard, it has been returned to its original numbering, BS 350.

In this revision, while interconversion factors between all the important units treated are given, the standpoint from which the various units and conversion factors are discussed is the SI. Very few imperial units remain in official use in the UK. Furthermore, the SI, under the custody of the General Conference of Weights and Measures (CGPM), forms the precise and natural basis for conversion information on units, and offers firm prospects of an international harmonization in unit practice, after which conversion factors will no longer be required. However, it is recognized that many older documents refer to units which are not recommended now, so conversion factors have been retained for many of these.

The standardization function of this standard lies in the provision of conversion factors reliable to a stated accuracy. Other important information is included to help the user to make conversions. BS 350 does not purport to define quantities or units, or to standardize the letter symbols or abbreviations used for units. These matters are dealt with elsewhere, but their mention is necessary here and has been updated with the latest international and national decisions.

Where conversion factors are given in bold type it is to show that they are exact; in general, factors have been rounded to include six significant figures, thus permitting accuracies satisfactory for most practical purposes. The computation of each factor has as far as possible been made from first principles, using eight or more significant figures to minimize the possibilities of errors in rounding. Six-figure factors are unnecessarily precise for many practical purposes, and may be rounded to fewer significant figures as appropriate. The Department of Trade and Industry has asked that users of these conversion factors be reminded that conversions for trade purposes have to be based on the statutory definitions of units in the Weights and Measures Act, 1985 [1].

Submission of additional units for inclusion in a future edition of the standard will be welcomed. These should be sent to the secretary of Technical Committee SS/7 at BSI, 389 Chiswick High Road, London W4 4AL.

This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

In particular, attention is drawn to the Weights and Measures Act 1985 [1] and associated Orders and Amendments.

Summary of pages

This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 105 and a back cover.

The BSI copyright notice displayed in this document indicates when the document was last issued.

BS 350:2004

Conversion factors for units

Current

Published:

25 May 2004