100 Gallon Propane Tank (420 lb) dimensions

Why it is called 100 gallons

"100 gallon" is the name the 420 lb cylinder is commonly sold under; Manchester's catalog calls it the 420 lb. Its 1,000 lb water capacity is about 120 gallons. DOT allows 42 % of that weight in propane, which is where 420 lb comes from, and 420 lb of propane at 4.24 lb per gallon is 99.1 gallons.

Manchester lists 95.9 gal of LPG capacity, which is 80 % of the water volume, the usual volumetric fill. Our 99.1 gal is 420 lb divided by propane's density at 60 °F. Either way, it holds about 100 gallons.

DOT cylinder or ASME tank

The same 30 in by 53.8 in shell is sold two ways. The DOT cylinder is built to specification 4BW240, and its 420 lb rating is a weight of propane. The ASME version is 13 lb heavier and is a stationary pressure vessel, filled on site to about 80 % of its 118 gal water capacity under NFPA 58.

From the outside they look alike. The data plate or collar stamp tells you which you have.

Propane left, in 10 % steps

Weigh the tank and subtract the TW stamped on it; 278 lb on the scale means it is empty. "Full" here is the 420 lb rated fill. A float gauge reads percent of water volume instead, so at this fill it shows about 83 %, not 100 %.

Hours from one fill

420 lb of propane is about 9.1 million Btu (EIA: 91,452 Btu per gallon). Divide by the combined Btu/h rating of the appliances it feeds to get hours.

Add up the Btu/h ratings of everything that can run at once to choose a row. For heating over a season, use the degree-day method in how long propane lasts.

Sources and standards

1. Steel Tanks & Cylinders for LP Gas Systems, Portable Steel Tanks Catalog 49501 (2020)Manchester Tank & Equipment Co.https://mcwane.com/upl/downloads/library/tanks-cylinders-for-lpg-systems-100lb-to-420lb.pdfThe manufacturer's catalog for 100 lb to 420 lb DOT cylinders and the matching vertical ASME tanks (28.6, 57 and 118 gal). Its 100 lb figures differ slightly from the newer Catalog 49500 (2022). 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 § 178.61 — Specification 4BW welded steel cylinders with electric-arc welded seamU.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-178.61The construction specification behind the “DOT 4BW240” marking on Manchester Tank’s 40 lb and larger cylinders.
4. 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.
5. 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.
6. 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.