{"data":{"id":"us/40-cfr-63.3","jurisdiction":"us","citation":"40 CFR 63.3","heading":"Units and abbreviations.","body":"Used in this part are abbreviations and symbols of units of measure. These are defined as follows:\n(a) System International (SI) units of measure:\nA = ampere\ng = gram\nHz = hertz\nJ = joule\n°K = degree Kelvin\nkg = kilogram\nl = liter\nm = meter\nm 3 = cubic meter\nmg = milligram = 10−3 gram\nml = milliliter = 10−3 liter\nmm = millimeter = 10−3 meter\nMg = megagram = 10 6 gram = metric ton\nMJ = megajoule\nmol = mole\nN = newton\nng = nanogram = 10−9 gram\nnm = nanometer = 10−9 meter\nPa = pascal\ns = second\nV = volt\nW = watt\nΩ = ohm\nµg = microgram = 10−6 gram\nµl = microliter = 10−6 liter\n(b) Other units of measure:\nBtu = British thermal unit\n°C = degree Celsius (centigrade)\ncal = calorie\ncfm = cubic feet per minute\ncc = cubic centimeter\ncu ft = cubic feet\nd = day\ndcf = dry cubic feet\ndcm = dry cubic meter\ndscf = dry cubic feet at standard conditions\ndscm = dry cubic meter at standard conditions\neq = equivalent\n°F degree Fahrenheit\nft = feet\nft 2 = square feet\nft 3 = cubic feet\ngal = gallon\ngr = grain\ng-eq = gram equivalent\ng-mole = gram mole\nhr = hour\nin. = inch\nin. H2 O = inches of water\nK = 1,000\nkcal = kilocalorie\nlb = pound\nlpm = liter per minute\nmeq = milliequivalent\nmin = minute\nMW = molecular weight\noz = ounces\nppb = parts per billion\nppbw = parts per billion by weight\nppbv = parts per billion by volume\nppm = parts per million\nppmw = parts per million by weight\nppmv = parts per million by volume\npsia = pounds per square inch absolute\npsig = pounds per square inch gage\n°R = degree Rankine\nscf = cubic feet at standard conditions\nscfh = cubic feet at standard conditions per hour\nscm = cubic meter at standard conditions\nscmm = cubic meter at standard conditions per minute\nsec = second\nsq ft = square feet\nstd = at standard conditions\nv/v = volume per volume\nyd 2 = square yards\nyr = year\n(c) Miscellaneous:\nact = actual\navg = average\nI.D. = inside diameter\nM = molar\nN = normal\nO.D. = outside diameter\n% = percent","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER C—AIR PROGRAMS","PART 63—NATIONAL EMISSION STANDARDS FOR HAZARDOUS AIR POLLUTANTS FOR SOURCE CATEGORIES","Subpart A—General Provisions"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"8674f814f1a1dafaf94bc0aa29df39fd49e2503aeadac93d471127b0507b03cd","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-63.2","next":"us/40-cfr-63.4"},"notice":"GroundRules: Original legal text. Not legal advice."}