Tank charts, inch by inch.

How to use a tank chart without fooling yourself

A tank chart answers one question: given a liquid depth measured from the inside bottom, how much is in the tank? Everything that goes wrong with charts goes wrong in the gap between that sentence and what people actually do.

• Measure from the inside bottom, not from a convenient edge. Not the fill-pipe rim, not the top of a riser, not the outside of the shell. On a buried tank the distance from grade to tank bottom is a number you should have written down at installation.
• Keep the stick vertical. An angled fill pipe does not excuse an angled stick. Ten degrees off vertical reads about 1.5 % long; twenty degrees reads 6 % long.
• Don't interpolate linearly on a round tank. In a horizontal cylinder the middle inches hold far more than the end inches, so averaging two distant chart rows is systematically wrong. Every chart here has a reader that computes the exact value instead.
• Half depth is not half volume on any tank with curved ends. Each chart page states the depth at which half that tank's volume actually sits.
• Subtract the water bottom. Water is denser than fuel and sits underneath. Your stick reads total depth; the chart converts total depth to total volume. Find the water line with water-finding paste and take it off before you call the rest product.

What a computed chart is, and what it isn't

Every value on these pages comes from a closed-form partial-fill formula applied to a stated geometry — circular segments for cylinders, a piecewise obround model for 275 and 330 gallon heating-oil tanks, and scaled spherical caps for dished heads. There is no interpolation and no curve fitting, and the tolerances are enforced by automated tests before each build. The methodology page shows the derivations.

That makes these charts exact for the geometry stated. It does not make them a calibration. A real tank has corner radii, internal ribs, plate thickness, a fabrication tolerance and usually a degree or two of tilt, and the difference against a manufacturer's own chart is typically 1–3 %. For operations, ordering and reconciliation that is fine. For custody transfer or a measurement that has to survive a dispute, the tank needs a capacity table produced by physical calibration under ISO 7507-1 or the equivalent API MPMS chapters, with corrections for plate thickness, shell expansion and tilt.

Where charts become a legal requirement

For underground fuel tanks, gauging is not optional record-keeping. Under 40 CFR § 280.43(a) inventory control must be capable of detecting a release of 1.0 % of flow-through plus 130 gallons in a month, deliveries must be reconciled against receipts, and the gauging equipment must resolve the full height of the tank to the nearest one-eighth of an inch. Manual tank gauging is permitted as the sole release-detection method only for tanks of 550 gallons or less nominal capacity, and for some 551–1,000 gallon tanks meeting the diameter criteria in § 280.43(b). State programmes approved under 40 CFR Part 281 are often stricter.

Propane is the exception on this site: a propane vessel is a sealed pressure vessel and must never be opened or stuck. Its chart pages exist so you can cross-check a suspect float gauge — which reads percent of water capacity, not gallons of propane — against a delivery ticket.

Propane tanks: reading the chart and the standards

Reading the gauge (don't stick a propane tank)

Propane vessels are sealed pressure vessels — you never open or stick them. Read the float gauge on top: it shows percent of water capacity, and gallons of propane = gauge % × water capacity. The inch table on each chart page is the underlying geometry, useful for cross-checking a suspect gauge against a delivery ticket. A stationary tank is filled to about 80 %, so a healthy gauge tops out around there after a delivery.

Why your reading may not match a chart

The arithmetic on each chart page is exact for the geometry it states. The disagreements you will actually see come from the tank and the measurement, not the maths — in roughly this order of size:

• The float gauge reads percent of water capacity, not gallons. Multiply the gauge percentage by the tank's water capacity to get gallons of propane. A gauge reading 40 % on a propane vessel is not 40 % of the propane you can legally carry.
• Float gauges are approximate by design. They are magnetic dial gauges with a float arm, typically accurate to a few percent, and they stick. A reading that has not moved in a week during heating season is a gauge fault until proven otherwise.
• Temperature moves the liquid level visibly. Propane's volumetric expansion coefficient is roughly six times water's. The same mass of propane reads noticeably higher on a hot afternoon than at dawn.
• Never open or stick a propane vessel. It is a sealed pressure vessel under roughly 100–200 psi in summer conditions. The inch table on each propane chart page is geometry for cross-checking a suspect gauge against a delivery ticket, not an invitation to gauge manually.

The standards behind propane tanks

This is set out once, on the tank sizes hub.

Common questions

Heating-oil tanks: reading the chart and the standards

How to stick heating-oil tanks

Remove the fill cap or the gauge fitting on top of the tank. Lower a clean, dry stick straight down until it gently touches the tank bottom — don't jab, sediment lives there. Hold it vertical for a second, lift it out, and read the wet line. That measurement, from the bottom of the stick to the wet/dry boundary, is the depth you enter in a chart page's reader. If your stick goes in through an angled fill pipe, make sure the stick itself ends up vertical inside the tank, or the reading will run long.

Why your reading may not match a chart

The arithmetic on each chart page is exact for the geometry it states. The disagreements you will actually see come from the tank and the measurement, not the maths — in roughly this order of size:

• The tank is not perfectly plumb. A 275 sitting on settled legs or an uneven pad leans, and the stick then reads long on the low side. Half an inch of lean across the width is easily a few gallons.
• Sludge and water on the bottom. Water is denser than oil and sits underneath. Your stick reads total depth; the chart converts total depth to total volume. If two inches of that is water, two inches of your reading is not fuel.
• Corner radii and internal ribs. The obround model the charts use is exact for the stated geometry, but a real welded tank has corner radii and internal stiffeners that remove a little volume — typically 1–3 % against a manufacturer's own chart.
• The stick is not vertical. Fill pipes on 275s are often offset or angled. A stick 10° off vertical reads about 1.5 % long; 20° off reads 6 % long.

The standards behind heating-oil tanks

This is set out once, on the tank sizes hub.

Underground oil tanks: reading the chart and the standards

How to stick underground oil tanks

Underground tanks are sticked through the fill pipe. Lower the stick until it rests on the tank bottom, then read the wet line — but remember the fill pipe riser adds length above the tank: your liquid depth is measured from the stick bottom to the wet line only, and it can never exceed the tank diameter. Two pro habits: smear water-finding paste on the bottom few inches of the stick once a season (it changes color if groundwater is intruding), and stick before and after a metered delivery once — if the chart agrees with the metered gallons, you've confirmed the tank size.

Why your reading may not match a chart

The arithmetic on each chart page is exact for the geometry it states. The disagreements you will actually see come from the tank and the measurement, not the maths — in roughly this order of size:

• Tank tilt is designed in. Buried tanks are commonly set with a deliberate slope so product drains toward one end. The chart assumes level, so a sloped tank reads high or low depending on which end the fill pipe is at. ISO 7507 and the API calibration standards include explicit tilt corrections for this reason.
• Water bottoms. Water accumulates under the fuel and is measured separately with water-finding paste. Subtract the water depth's volume from the total before you call the rest product.
• The drop tube and riser add height that is not tank. Measure to the tank bottom, and know how far below grade that is — a stick that bottoms out on a riser shoulder will read consistently short and look like a slow leak.
• Thermal movement between the delivery and the gauge. Fuel delivered warm and gauged cold has shrunk. On a 1,000 gallon tank a 15 °F drop is roughly 7 gallons of apparent loss with nothing actually missing.

The standards behind underground oil tanks

This is set out once, on the tank sizes hub.

Common questions

IBC totes and drums: reading the chart and the standards

How to measure IBC totes and drums

Measure liquid depth from the inside bottom, straight up to the surface, with a clean rule or stick held vertical. For IBC totes, the molded gallon/liter markings on the bottle are more accurate near the corners than any rectangular model — use the chart for in-between readings and the markings as your anchor points.

Common questions

IBC totes: reading the chart and the standards

Why your reading may not match a chart

The arithmetic on each chart page is exact for the geometry it states. The disagreements you will actually see come from the tank and the measurement, not the maths — in roughly this order of size:

• The moulded markings beat any model. IBC bottles are blow-moulded with rounded corners and a tapered base, and the manufacturer's own graduations account for that shape. Use the markings as your anchor points and the chart for the depths in between.
• Nominal 275 and 330 are cage sizes, not fill volumes. A '275 gallon' tote is built around a nominally 1,000-litre bottle, and its rated capacity is stamped in the UN marking — that number, not the label, is the one that governs.
• Bottles bulge under load. A full tote's walls deflect outward inside the cage, which is why a stacked tote's level reads slightly differently from a standing one.
• Totes are rarely level. They sit on pallets, on uneven concrete, on forklift tines. A degree of tilt across a 40-inch footprint is most of an inch of error.

The standards behind IBC totes

This is set out once, on the tank sizes hub.

Aquariums: measuring and rated size

How to measure your water volume

Measure from the inside glass bottom up to the water line — not the trim, and not from outside (glass thickness inflates the reading on small tanks). If you have substrate, measure from the top of the substrate instead and you'll get the actual water volume above it, which is the number that matters for dosing and stocking. Rated tank sizes are brim-full nominal; a typical running setup holds 10–15% less.

Why your reading may not match a chart

The arithmetic on each chart page is exact for the geometry it states. The disagreements you will actually see come from the tank and the measurement, not the maths — in roughly this order of size:

• Rated size is a marketing round number. Trade sizes are brim-full nominal and based on exterior dimensions. Real water volume in a running tank is commonly 10–15 % below the label once you subtract the air gap, the trim and the glass.
• Substrate displaces water. Two inches of gravel across the footprint removes roughly two inches of water volume, less the pore space the water fills — usually counted as 60–70 % of the substrate's bulk volume displaced.
• Rock and hardscape displace more than they look like. Weigh dry rock and divide by its density, or measure the water it displaces in a bucket. Estimating by eye reliably undercounts.
• Glass thickness inflates outside measurements. On a small tank, ¼-inch glass on both sides of a 12-inch width removes 4 % of the footprint. Measure inside.

What governs an aquarium's rated size

This is set out once, on the tank sizes hub.

Common questions

Notes that apply to every chart

Common questions

Sources and standards

These are the documents behind the units, the codes and the calibration practice referenced across the chart library. Individual chart pages cite the subset that applies to that tank.

1. Handbook 44, Appendix C — General Tables of Units of MeasurementNational Institute of Standards and Technology, U.S. Department of Commercehttps://www.nist.gov/document/2026-nist-handbook-44-appendix-cThe legal-metrology reference for U.S. customary units. Fixes the U.S. liquid gallon at exactly 231 cubic inches and tabulates the full liquid-volume chain (minim → fluid dram → fluid ounce → gill → pint → quart → gallon).
2. Special Publication 811, Appendix B.8 — Factors for Units Listed AlphabeticallyNational Institute of Standards and Technologyhttps://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8NIST's master table of conversions into SI. Factors printed in boldface are exact by definition rather than measured or rounded — which is how you tell a defined unit from an approximated one.
3. 40 CFR § 280.43 — Methods of release detection for tanksU.S. Environmental Protection Agency, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-280/subpart-D/section-280.43The federal rule that makes tank charts a compliance instrument rather than a convenience. Inventory control must detect a release of 1.0 % of flow-through plus 130 gallons per month; gauging equipment must read the full tank height to the nearest one-eighth of an inch; manual tank gauging is allowed as the sole release-detection method only for tanks of 550 gallons or less (and some 551–1,000 gallon tanks meeting the diameter criteria).
4. 40 CFR Part 280 — Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage TanksU.S. Environmental Protection Agency, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-40/chapter-I/subchapter-I/part-280The whole federal UST programme: design and construction standards (§ 280.20), release detection (Subpart D), operator training and closure. State programmes approved under Part 281 may be stricter.
5. ISO 7507-1 — Petroleum and liquid petroleum products: Calibration of vertical cylindrical tanks, Part 1: Manual strapping methodInternational Organization for StandardizationPaid standard — cited by designation; obtain from the publisher.Defines how a tank's capacity table (its “strapping table”) is produced from physical measurement, including corrections for plate thickness, shell expansion and tank tilt. It is the reason a real tank's chart rarely matches naive geometry to the last gallon.
6. Manual of Petroleum Measurement Standards (MPMS) — Ch. 1 “Vocabulary”, Ch. 11.1 “Temperature and Pressure Correction Factors”, Ch. 12.1 “Calculation of Static Petroleum Quantities”American Petroleum Institute (with ASTM D1250 / ISO 91 volume correction tables)Paid standard — cited by designation; obtain from the publisher.The industry standard for turning a gauged tank volume into a traded quantity: observed volume, gross standard volume at 60 °F, and net standard volume after sediment and water. A unit conversion is only the first step of that chain.
7. 29 CFR § 1910.110 — Storage and handling of liquefied petroleum gases (Table H-23, minimum distances)U.S. Occupational Safety and Health Administration, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-29/subtitle-B/chapter-XVII/part-1910/subpart-H/section-1910.110Federal separation distances for LP-gas containers, by water capacity: under 125 gal — 10 ft above ground; 125–250 gal — 10 ft; 251–500 gal — 10 ft and 3 ft between containers; 501–2,000 gal — 25 ft (reducible to 10 ft for a single container of 1,200 gal water capacity or less, if it is at least 25 ft from any other LP-gas container over 125 gal); 2,001–30,000 gal — 50 ft.
8. 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.
9. NFPA 31 — Standard for the Installation of Oil-Burning EquipmentNational Fire Protection AssociationPaid standard — cited by designation; obtain from the publisher.Governs how fuel-oil supply tanks are installed, vented, filled and located, including tank-to-appliance clearances and fill and vent piping. Adopted, often with amendments, by most US states.
10. UL 80 — Standard for Steel Tanks for Oil-Burner Fuel and Other Combustible Liquids; UL 58 — Steel Underground Tanks for Flammable and Combustible LiquidsUL Standards & EngagementPaid standard — cited by designation; obtain from the publisher.The construction standards behind the familiar 275 and 330 gallon aboveground heating-oil tanks (UL 80) and steel USTs (UL 58). They govern steel gauge, seams, fittings and leak testing — not gauge-chart accuracy, which is why a listed tank still needs its own capacity table for anything measured.
11. 49 CFR § 178.504 — Standards for steel drums (and § 178.502, identification codes)U.S. Pipeline and Hazardous Materials Safety Administration, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-178/subpart-L/section-178.504The current federal standard for steel drums. Codes are 1A1 (non-removable head) and 1A2 (removable head); openings over 3 inches make a drum removable-head by definition. The legacy DOT-17E designation was superseded by these UN performance-oriented standards.
12. 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.
13. International Residential Code, Table R301.5 — Minimum uniformly distributed live loadsInternational Code Council (free read-only access at codes.iccsafe.org)https://codes.iccsafe.org/s/IRC2021P2/chapter-3-building-planning/IRC2021P2-Pt03-Ch03-SecR301.5Residential floors are designed to 40 lb/ft² live load in habitable rooms other than sleeping rooms, and 30 lb/ft² in sleeping rooms. A filled aquarium concentrates far more than that over its own footprint, which is why the comparison is worth doing before siting one upstairs.
14. 49 CFR Part 178 — Specifications for Packagings (Subpart N: Intermediate Bulk Containers)U.S. Pipeline and Hazardous Materials Safety Administration, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-C/part-178Design, construction, marking and periodic retest requirements for IBCs. The UN marking moulded into a tote's bottle records its design type, packing group, test date and rated capacity — read it before trusting a nominal gallon figure.
15. 40 CFR § 112.8(c)(2) — Spill Prevention, Control, and Countermeasure Plan requirements for onshore facilitiesU.S. Environmental Protection Agency, via the electronic Code of Federal Regulationshttps://www.ecfr.gov/current/title-40/chapter-I/subchapter-D/part-112/subpart-B/section-112.8Requires secondary containment sized for the entire capacity of the largest single container, plus sufficient freeboard to contain precipitation. Note that the rule itself does not state “110 %” — that is a common design convention layered on top of the regulatory floor.

Every linked source above was retrieved and checked on 2026-09-02. Factors quoted as exact are exact by definition in the cited document, not rounded by us.