20 lb Propane Tank dimensions & weight

What the 20 means

The 20 is pounds of propane, not the size or weight of the tank. DOT limits a propane cylinder to 42 % of its water capacity by weight, and 42 % of this cylinder's 47.6 lb water capacity is 20.0 lb.

So a "full" 20 lb cylinder holds about 4.7 gallons of liquid. The rest of the space is vapour, which gives the liquid room to expand on a hot day.

How much propane is left

Stand the cylinder on a bathroom or luggage scale and find the reading below. The table assumes Manchester's 18 lb tare; if the TW stamped on your collar is different, add or subtract the difference from every scale reading.

Gallons = pounds ÷ 4.24, the density of liquid propane at 60 °F on our methodology page.

How long it runs

A full 20 lb cylinder holds about 431,000 Btu: 20 lb × 21,569 Btu per lb, which is EIA's 91,452 Btu per gallon divided by 4.24 lb per gallon. Divide by the burner's rating to get hours.

These are hours at the full rating printed on the appliance. An appliance that cycles or runs below its rating uses less per hour and lasts longer.

Sizes either side

The 20 lb sits in a run of cylinders that share its 12.2 in diameter; mostly the height changes.

Every size from 5 to 420 lb is on the cylinder sizes page.

Reading the collar

• TW is the tare weight of your cylinder. Use it, not a spec sheet, when you weigh the tank.
• WC is water capacity in pounds: 47.6 lb on Manchester's 20 lb cylinder.
• DOT-4BA240 is the construction specification, 49 CFR § 178.51, followed by the service pressure, 240 psig, as § 178.35(f) requires.
• A month and year is the test date. 49 CFR § 180.209 sets how long after it the cylinder must be requalified.
• OPD. Manchester's sheet lists an overfilling prevention device on its 5 to 40 lb cylinders, so this one has one.

Sources and standards

1. DOT 5 lb. - 100 lb. Catalog 49500 (09/2022)Manchester Tank & Equipment Co.https://www.mantank.com/upl/downloads/content-blocks/portable-dot-lpg-cylinders-5lb-to-100lb.pdfThe manufacturer's published figures for each cylinder size: LPG capacity in gallons, water capacity in pounds, overall height, diameter, tare weight and DOT specification, and that its 5 to 40 lb cylinders have an overfilling prevention device (OPD). Checked 2026-10-22.
2. 49 CFR § 173.304a — Additional requirements for shipment of liquefied compressed gases (filling densities)U.S. Department of Transportation (PHMSA), via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-173/subpart-G/section-173.304aParagraph (d)(1) sets the maximum filling density for liquefied petroleum gas by its specific gravity at 60 °F. For 0.504–0.510, the band propane falls in, it is 42 percent of the cylinder’s water capacity by weight — which is where the 20, 100 and 420 lb ratings come from.
3. 49 CFR § 178.51 — Specification 4BA welded or brazed steel cylindersU.S. Department of Transportation (PHMSA), via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-178/subpart-C/section-178.51The construction specification behind the “DOT 4BA240” marking on small propane cylinders. Under § 178.35(f)(1)(i) the specification is followed by the service pressure, here 240 psig.
4. 49 CFR § 180.209 — Requirements for requalification of specification cylindersU.S. Department of Transportation (PHMSA), via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-180/subpart-C/section-180.209Sets how often a DOT cylinder must be requalified before it can be refilled. The interval depends on the method used (hydrostatic test or visual inspection), and is counted from the test date stamped on the cylinder.
5. NFPA 58 — Liquefied Petroleum Gas Code (separation distances, Table 6.4.1.1; filling limits, Ch. 7)National Fire Protection AssociationPaid standard — cited by designation; obtain from the publisher.The model code most US states adopt for propane installations, and the one your local inspector is most likely working from. It is not identical to OSHA's Table H-23 — notably for containers of 125 gal water capacity and under — so confirm which is enforced locally. NFPA publishes free read-only access to its codes at nfpa.org.
6. Thermal Conversion Factors — Monthly Energy Review, Appendix A (source documentation)U.S. Energy Information Administrationhttps://www.eia.gov/totalenergy/data/monthly/pdf/mer_a_doc.pdfWhere the Btu-per-gallon figures come from and how they were derived. Distillate fuel oil is 5.770 million Btu/bbl at 15 ppm sulfur and under, 5.817 at 15–500 ppm and 5.825 above 500 ppm — 137,400, 138,500 and 138,700 Btu per gallon respectively. Propane is 3.841 million Btu/bbl, or 91,452 Btu per gallon, estimated by EIA from NIST Chemistry WebBook enthalpy-of-combustion data and liquid density at 60 °F.
7. Methodology — the partial-fill formulas and liquid densities used on this sitetankvolumecalc.comhttps://tankvolumecalc.com/methodology/Every chart value here comes from a closed-form partial-fill formula, not interpolation: circular segments for cylinders, a piecewise obround model for 275/330 heating-oil tanks, and scaled spherical caps for dished heads. Densities and their bases are tabulated there.

The manufacturer sheets and 49 CFR sections above were retrieved and checked on 2026-10-22; the other linked sources on 2026-09-02.