1247:
265:, while its symbol ("Torr") is always written with an uppercase initial; including in combinations with prefixes and other unit symbols, as in "mTorr" (millitorr) or "Torr⋅L/s" (torr-litres per second). The symbol (uppercase) should be used with prefix symbols (thus, mTorr and millitorr are correct, but mtorr and milliTorr are not).
284:
to the general public. He is credited with giving the first modern explanation of atmospheric pressure. Scientists at the time were familiar with small fluctuations in height that occurred in barometers. When these fluctuations were explained as a manifestation of changes in atmospheric pressure, the
292:
Over time, 760 millimeters of mercury at 0 °C came to be regarded as the standard atmospheric pressure. In honour of
Torricelli, the torr was defined as a unit of pressure equal to one millimeter of mercury at 0 °C. However, since the acceleration due to gravity – and thus the weight of a
353:
that depend on an assumed density of a fluid and an assumed acceleration due to gravity. The use of these units is discouraged. Nevertheless, manometric units are routinely used in medicine and physiology, and they continue to be used in areas as diverse as weather reporting and scuba diving.
495:
The difference between one millimeter of mercury and one torr, as well as between one atmosphere (101.325 kPa) and 760 mmHg (101.3250144354 kPa), is less than one part in seven million (or less than 0.000015%). This small difference is negligible for all practical purposes.
565:
These four pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures. The torr is used in high-vacuum physics and engineering.
328:
of one atmosphere. This yields a precise definition that is unambiguous and independent of measurements of the density of mercury or the acceleration due to gravity on Earth.
362:
The millimeter of mercury by definition is 133.322387415 Pa (13.5951 g/cm × 9.80665 m/s × 1 mm), which is approximated with known accuracies of density of mercury and
305:
1084:
Devices similar to the modern barometer, using water instead of mercury, were studied by a number of scientists in the early 1640s (see
272:, the unit measuring the strength of a magnetic field. Although frequently encountered, the alternative spelling "Tor" is incorrect.
591:
1088:). Torricelli's explanation of the principle of the barometer appears in a letter to Michelangelo Ricci dated 11 June 1644.
1215:
1194:
337:
1246:
385:
of one standard atmosphere, while the atmosphere is defined as 101325 pascals. Therefore, 1 Torr is equal to
1148:
224:
1267:
1161:
1051:
584:
133:
1277:
1272:
1237:
1173:
Note that a pressure of 1 bar (100000 Pa) is slightly less than a pressure of 1 atmosphere (101325 Pa).
616:
1198:
577:
626:
242:
57:
216:
151:
20:
268:
The torr is sometimes incorrectly denoted by the symbol "T", which is the SI symbol for the
611:
220:
8:
1041:
1036:
293:
column of mercury – is a function of elevation and latitude (due to the rotation and non-
281:
1211:
1190:
1131:
1031:
188:
82:
223:
made them slightly different (by less than 0.000015%). The torr is not part of the
363:
1186:
1085:
1046:
114:
1251:
1098:
168:
1261:
1061:
1056:
601:
309:
245:, an Italian physicist and mathematician who discovered the principle of the
228:
208:
123:
1230:
280:
Torricelli attracted considerable attention when he demonstrated the first
269:
286:
262:
164:
308:
to the currently accepted definition: one atmosphere is equal to 101325
1119:
606:
294:
246:
434:
The relationship between the torr and the millimeter of mercury is:
297:
of the Earth), this definition is imprecise and varies by location.
1066:
428:
39:
1210:
DeVoe H. Thermodynamics and
Chemistry. Prentice-Hall, Inc., 2001,
499:
In the
European Union, the millimeter of mercury is defined as
561:
The atmosphere (symbol: atm), defined as 101.325 kPa exactly.
231:
215:
Historically, one torr was intended to be the same as one "
427:) is an infinitely long, periodically repeating decimal (
1235:
338:
Pressure measurement § Liquid column (manometer)
1145:
BS 350: Part 1: 1974 – Conversion factors and tables
1187:
Quantities, Units and
Symbols in Physical Chemistry
558:The bar (symbol: bar), defined as 100 kPa exactly.
252:
1259:
331:
306:10th General Conference on Weights and Measures
585:
401: Pa. The decimal form of this fraction (
227:(SI). Even so, it is often combined with the
1189:, 3rd ed. Royal Society of Chemistry, 2007
1132:National Physical Laboratory: Pressure units
219:", but subsequent redefinitions of the two
592:
578:
191:(101325 Pa). Thus one torr is exactly
1260:
134:British Gravitational System
357:
1120:BIPM – Resolution 4 of the 10th CGPM
13:
14:
1289:
1224:
554:Other units of pressure include:
312:. The torr was then redefined as
1245:
1018:
940:
855:
788:
727:
655:
300:In 1954, the definition of the
1204:
1176:
1167:
1155:
1137:
1125:
1113:
1091:
1078:
253:Nomenclature and common errors
1:
1149:British Standards Institution
1099:"Rules and style conventions"
1072:
225:International System of Units
1162:Council directive 80/181/EEC
1052:Outline of the metric system
332:Manometric units of pressure
238:(mTorr) or 0.001 Torr.
16:Traditional unit of pressure
7:
1025:
10:
1294:
335:
275:
18:
573:
241:The unit was named after
129:
110:
106:
88:
63:
53:
45:
35:
30:
1086:History of the Barometer
369:The torr is defined as
347:millimeters of mercury
243:Evangelista Torricelli
58:Evangelista Torricelli
627:Pound per square inch
217:millimeter of mercury
171:, defined as exactly
21:Torr (disambiguation)
1231:NPL – pressure units
612:Technical atmosphere
351:centimeters of water
212:(≈ 133.32 Pa).
163:(symbol: Torr) is a
19:For other uses, see
1268:Non-SI metric units
1151:. 1974. p. 49.
1042:Conversion of units
1037:Centimetre of water
617:Standard atmosphere
570:
503:1 mmHg = 133.322 Pa
304:was revised by the
101:... is equal to ...
1164:(20 December 1979)
568:
358:Conversion factors
345:are units such as
139:
131:
120:
112:
1278:Mercury (element)
1273:Units of pressure
1182:Cohen E. R.
1032:Atmosphere (unit)
1023:
1022:
282:mercury barometer
157:
156:
89:Conversions
1285:
1250:
1249:
1241:
1219:
1208:
1202:
1180:
1174:
1171:
1165:
1159:
1153:
1152:
1141:
1135:
1129:
1123:
1117:
1111:
1110:
1108:
1106:
1095:
1089:
1082:
1016:
1015:
1012:
1005:
1004:
1001:
994:
993:
990:
983:
982:
979:
972:
971:
968:
964:
952:
951:
948:
938:
937:
934:
928:
926:
925:
922:
919:
911:
910:
907:
900:
899:
896:
889:
888:
885:
873:
872:
869:
866:
853:
848:
847:
839:
838:
825:
824:
821:
818:
811:
810:
803:
802:
799:
796:
786:
785:
778:
776:
764:
763:
760:
757:
749:
743:
742:
734:
725:
714:
713:
710:
707:
704:
695:
693:
684:
682:
673:
671:
662:
594:
587:
580:
571:
567:
549:
548:
545:
540:
528:
527:
524:
519:
490:
489:
486:
481:
476:
471:
462:
461:
458:
453:
448:
443:
426:
425:
424:
423:
422:
419:
416:
413:
410:
400:
398:
397:
394:
391:
384:
382:
381:
378:
375:
364:standard gravity
343:Manometric units
327:
325:
324:
321:
318:
211:
207:
205:
204:
201:
198:
186:
184:
183:
180:
177:
165:unit of pressure
149:
148:
145:
140:
132:
121:
115:SI derived units
113:
81:
79:
78:
75:
72:
28:
27:
1293:
1292:
1288:
1287:
1286:
1284:
1283:
1282:
1258:
1257:
1256:
1244:
1236:
1227:
1222:
1209:
1205:
1181:
1177:
1172:
1168:
1160:
1156:
1143:
1142:
1138:
1130:
1126:
1118:
1114:
1104:
1102:
1097:
1096:
1092:
1083:
1079:
1075:
1047:Inch of mercury
1028:
1013:
1010:
1008:
1002:
999:
997:
991:
988:
986:
980:
977:
975:
969:
966:
962:
960:
949:
946:
944:
935:
932:
930:
923:
920:
917:
916:
914:
908:
905:
903:
897:
894:
892:
886:
883:
881:
870:
867:
864:
862:
851:
845:
843:
836:
834:
822:
819:
816:
814:
808:
806:
800:
797:
794:
792:
783:
781:
774:
772:
761:
758:
755:
753:
747:
740:
738:
732:
723:
711:
708:
705:
702:
700:
691:
689:
680:
678:
669:
667:
660:
598:
569:Pressure units
546:
541:
535:
533:
525:
520:
514:
512:
487:
482:
477:
472:
469:
467:
459:
454:
449:
444:
441:
439:
420:
417:
414:
411:
408:
406:
405:
404:
402:
395:
392:
389:
388:
386:
379:
376:
373:
372:
370:
360:
340:
334:
322:
319:
316:
315:
313:
278:
255:
202:
199:
196:
195:
193:
192:
181:
178:
175:
174:
172:
146:
143:
141:
138:
130:
119:
111:
76:
73:
70:
69:
67:
24:
17:
12:
11:
5:
1291:
1281:
1280:
1275:
1270:
1255:
1254:
1234:
1233:
1226:
1225:External links
1223:
1221:
1220:
1203:
1199:IUPAC pdf copy
1175:
1166:
1154:
1136:
1124:
1112:
1090:
1076:
1074:
1071:
1070:
1069:
1064:
1059:
1054:
1049:
1044:
1039:
1034:
1027:
1024:
1021:
1020:
1017:
1006:
995:
984:
973:
958:
957:1 lbf/in
954:
953:
942:
939:
912:
901:
890:
879:
875:
874:
860:
857:
854:
849:
840:
831:
827:
826:
812:
804:
790:
787:
779:
770:
766:
765:
750:
744:
735:
729:
726:
721:
717:
716:
697:
686:
675:
664:
657:
654:
650:
649:
646:
643:
640:
637:
634:
630:
629:
624:
619:
614:
609:
604:
599:
597:
596:
589:
582:
574:
563:
562:
559:
552:
551:
530:
505:
504:
493:
492:
464:
359:
356:
333:
330:
277:
274:
261:is written in
257:The unit name
254:
251:
187:of a standard
169:absolute scale
155:
154:
136:
127:
126:
122:133.3224
117:
108:
107:
104:
103:
98:
91:
90:
86:
85:
65:
61:
60:
55:
51:
50:
47:
43:
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37:
33:
32:
15:
9:
6:
4:
3:
2:
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1279:
1276:
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1271:
1269:
1266:
1265:
1263:
1253:
1248:
1243:
1242:
1239:
1232:
1229:
1228:
1217:
1216:0-02-328741-1
1213:
1207:
1200:
1196:
1195:0-85404-433-7
1192:
1188:
1185:
1179:
1170:
1163:
1158:
1150:
1146:
1140:
1133:
1128:
1121:
1116:
1100:
1094:
1087:
1081:
1077:
1068:
1065:
1063:
1062:Pressure head
1060:
1058:
1057:Pascal (unit)
1055:
1053:
1050:
1048:
1045:
1043:
1040:
1038:
1035:
1033:
1030:
1029:
1007:
996:
985:
974:
959:
956:
955:
943:
913:
902:
891:
880:
877:
876:
861:
858:
850:
841:
832:
829:
828:
813:
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736:
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722:
719:
718:
698:
687:
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544:
539:
531:
523:
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510:
509:
508:
502:
501:
500:
497:
485:
480:
475:
465:
457:
452:
447:
437:
436:
435:
432:
431:length: 18).
430:
367:
365:
355:
352:
348:
344:
339:
329:
311:
307:
303:
298:
296:
290:
288:
283:
273:
271:
266:
264:
260:
250:
248:
244:
239:
237:
233:
230:
229:metric prefix
226:
222:
218:
213:
210:
190:
170:
166:
162:
153:
137:
135:
128:
125:
118:
116:
109:
105:
102:
99:
97:
93:
92:
87:
84:
66:
62:
59:
56:
52:
48:
44:
41:
38:
34:
29:
26:
22:
1206:
1183:
1178:
1169:
1157:
1144:
1139:
1127:
1115:
1105:29 September
1103:. Retrieved
1093:
1080:
878:1 Torr
621:
564:
553:
542:
537:
521:
516:
506:
498:
494:
483:
478:
473:
455:
450:
445:
433:
368:
361:
350:
346:
342:
341:
301:
299:
291:
279:
267:
258:
256:
240:
235:
234:to name one
214:
167:based on an
160:
158:
100:
95:
94:1 Torr
36:Unit of
25:
830:1 atm
720:1 bar
287:meteorology
285:science of
54:Named after
1262:Categories
1073:References
769:1 at
653:1 Pa
336:See also:
302:atmosphere
295:sphericity
289:was born.
263:lower case
189:atmosphere
64:Definition
648:(lbf/in)
532:1 mmHg =
511:1 Torr =
466:1 mmHg =
438:1 Torr =
249:in 1644.
247:barometer
236:millitorr
1067:Pressure
1026:See also
429:repetend
40:pressure
1252:Physics
927:
915:
882:133.322
807:735.559
715:lbf/in
699:1 Pa =
688:1 Pa =
677:1 Pa =
666:1 Pa =
659:1 Pa =
645:(Torr)
403:133.322
399:
387:
383:
371:
326:
314:
310:pascals
276:History
209:pascals
206:
194:
185:
173:
80:
68:
1238:Portal
1214:
1193:
1184:et al.
1101:. NIST
1009:51.714
863:14.695
852:1.0332
815:14.223
754:14.503
748:750.06
733:1.0197
690:7.5006
679:9.8692
668:1.0197
642:(atm)
636:(bar)
602:Pascal
507:hence
390:101325
197:101325
150:
96:in ...
46:Symbol
998:0.068
987:0.070
976:0.068
945:0.019
931:0.001
904:0.001
893:0.001
844:1.013
793:0.967
782:0.980
739:0.986
701:0.000
696:Torr
639:(at)
633:(Pa)
534:0.999
513:1.000
468:1.000
440:0.999
270:tesla
232:milli
221:units
142:0.019
1212:ISBN
1191:ISBN
1107:2012
965:.757
871:5142
859:760
823:1203
809:2401
801:3541
685:atm
663:bar
622:Torr
550:Torr
529:mmHg
491:Torr
463:mmHg
259:torr
161:torr
159:The
49:Torr
31:torr
1014:572
1011:932
1003:964
1000:045
992:958
989:306
981:573
978:947
970:168
967:293
963:894
950:775
947:336
936:789
933:315
924:760
906:359
898:224
895:333
887:421
884:368
868:775
865:948
837:325
835:101
820:307
817:343
798:105
795:841
784:665
775:066
762:022
759:773
756:773
712:730
709:737
706:037
703:145
674:at
607:Bar
547:...
543:236
526:...
522:763
488:...
484:321
479:466
474:142
470:000
460:...
456:699
451:533
446:857
442:999
421:947
418:578
415:631
412:052
409:421
407:368
396:760
380:760
349:or
323:760
203:760
182:760
152:psi
144:336
83:atm
77:760
1264::
1201:).
1147:.
1019:—
941:—
929:≈
909:51
856:—
846:25
842:≡
833:≡
789:—
777:.5
773:98
752:=
746:=
741:92
737:=
731:=
728:—
724:10
694:10
683:10
672:10
661:10
656:—
536:99
515:00
366:.
147:77
124:Pa
1240::
1218:.
1197:(
1134:.
1122:.
1109:.
961:6
921:/
918:1
692:×
681:×
670:×
593:e
586:t
579:v
538:7
517:2
393:/
377:/
374:1
320:/
317:1
200:/
179:/
176:1
74:/
71:1
23:.
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