How Much Oil Is Left in My Tank? (The Stick Method)

Float gauges fail slowly and lie politely. The stick method takes two minutes and doesn't.

Take a clean, dry stick longer than your tank is deep — a yardstick works for a 275. Remove the fill cap or gauge fitting, lower the stick straight down until it gently touches bottom, hold it vertical for a second, and pull it out. The boundary between wet and dry is your liquid depth.

Now convert inches to gallons with the right chart for your tank and orientation. On a standard 275 vertical, useful anchors are: 8 inches ≈ 37 gallons, 16 inches ≈ 92, 22 inches (half depth) ≈ 134, 31 inches ≈ 197. Our interactive 275V chart gives any reading to the quarter inch.

When should you order? Most suppliers recommend calling at a quarter tank — about 12 inches on a 275 vertical. Below that you risk drawing sediment from the tank bottom into the fuel line, and in cold snaps delivery slots fill up fast.

To know how much to order: gallons to order ≈ fill target − current. If your supplier fills a 275 to 250 gallons and your stick says 90, order about 160. Round down — a delivery that trips the whistle early is annoying for everyone.

The procedure, step by step

1. Pick the stick. Clean, dry, straight, and longer than the tank is deep. A yardstick clears a 275 or 330 vertical (44 inches) with room to grip. Wood or painted metal both work; what matters is that the wet line is readable against it.
2. Open the right fitting. The fill cap or the gauge fitting on top. Not the vent — the vent is not a measuring port and opening it risks the whistle assembly.
3. Lower slowly to the bottom. Let it touch, don't jab. Sediment lives on the floor of every tank over about five years old, and stirring it is how you end up changing a fuel filter in February.
4. Hold vertical, count three, withdraw. The oil needs a moment to wet the stick cleanly. Pull it straight up so the wet line doesn't smear.
5. Read the boundary, not the sheen. Oil climbs the stick slightly by capillary action. Read the crisp line, not the top of the film.
6. Take a second reading. Wipe the stick, repeat, and average. If the two differ by more than a quarter inch, something moved — the tank, your hand, or the surface — and a third reading settles it.

That last step is the one people skip and the one the professionals never do. The federal rule for manual tank gauging on regulated tanks specifies readings “based on an average of two consecutive stick readings” for exactly this reason: a single stick reading has more scatter than the chart's arithmetic ever will.

Inches to gallons on the common tanks

Anchors worth memorising for the two tanks in most basements. Full inch-by-inch tables are on the 275V and 330V chart pages, which read to the quarter inch.

Note how uneven the bottom is. The first eight inches of a 275 hold 37 gallons; the eight inches from 22 to 30 hold 56. The tank is obround — flat sides with a semicircular bottom of 13.5-inch radius — so the inches near the floor are worth much less than the ones in the middle. Anyone estimating linearly overestimates a nearly-empty tank, which is precisely the wrong direction to be wrong in.

When to order, and why the answer is not a fraction

“A quarter tank” is the common advice and it is a poor rule, because a quarter of a 275 is 12 inches in mild weather and 12 inches in a cold snap, but those are two completely different amounts of time. Order on days of supply, not on fraction of tank:

• Work out your gallons per day from two stick readings a week or two apart.
• Divide your current gallons by that rate.
• Order when that number drops below your supplier's worst-case lead time — which in a January cold snap is not the two days they quote in October.

There is a floor as well as a clock. Below roughly four inches on a 275 you are drawing from the zone where sediment and any water bottom sit, and the pickup on older installations sits low enough to find both.

Sources and standards

Where a standard genuinely governs what you should do here, it is cited and linked. Sticking a domestic tank is not a regulated activity, so this list is short by design — the practice references are here because they describe the method well, not because they bind you.

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. 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.
3. API MPMS Chapter 3.1A — Standard Practice for the Manual Gauging of Petroleum and Petroleum ProductsAmerican Petroleum InstitutePaid standard — cited by designation; obtain from the publisher.The reference practice for exactly what these guides describe: innage and outage gauging with a tape and bob, cutting the water line with water-finding paste, and taking repeat readings rather than trusting one. It is the reason a careful stick reading outranks a float gauge in any measurement hierarchy.
4. 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).

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.