Oil Tank Charts & Dip Tables — 275, 330, 500, 550, 1000 Gallon

Tanks of the same nominal gallon rating can have different exact dimensions. A '275 gal' heating-oil tank from one brand might measure 58 × 44 × 27 inches while another is 60 × 42 × 28 inches. Both round to 275 gallons on the sticker but their dip charts differ by several gallons at key readings. The charts in this guide use the most common industry dimensions for each class. For a certified dip chart specific to your tank, you need either a professional strapping service (they physically measure the tank's volume at each inch of depth) or to enter your exact inside dimensions into the dip chart generator on the calculator home page.

Lower a clean gauge stick straight down until it touches the bottom of the tank. Mark the level of liquid on the stick with a glove or your thumbnail, pull it out, and read the wet depth in inches. For horizontal tanks, measure straight down from the top shell to the bottom shell — not from the fill port, which is usually offset. Read the inches, then look up gallons in the dip chart. Before any delivery or tax-reporting dip reading, subtract the 'dead space' — the bottom few inches where the outlet pipe sits. For most heating-oil tanks this is about 1–1.5 inches. For propane tanks, subtract the fixed dip tube extension (usually stamped on the tank) because the tube opens above the bottom, leaving liquid below it that the system cannot draw.

Because the horizontal tank's cross-section is a circle, and circles are narrow at the bottom. At exactly a quarter of the diameter (25% depth), the chord slices off only the thin crescent-shaped segment at the very bottom of the circle. That crescent occupies only about 19.6% of the full circle's area. The formula: segment area A = r² × arccos((r-h)/r) - (r-h) × √(2rh-h²). For h = 0.25D (quarter depth), A/circle_area ≈ 0.196. By symmetry, three-quarters depth holds about 80% of capacity. Only at exactly half depth — where the circle is perfectly symmetric — does depth equal volume. This is the fundamental reason you cannot divide total gallons by inches of diameter to make a straight-line dip chart.

They are the same document. Dip chart and strapping table are the two most common field names — 'strapping' comes from the old practice of physically measuring (strapping) the tank at each inch of depth with a surveyor's tape and converting the measured segment area to volume. Calibration table is the more formal engineering name, especially when certified for custody transfer (like fuel deliveries). All three terms describe a depth-to-volume lookup table, usually in 1-inch increments, used to convert a gauge-stick reading to gallons. The free dip chart generator on the home page produces a mathematically computed version of this document; certified charts require physical measurement by a licensed tank calibration service.

Because a vertical cylinder has the same circular cross-section at every height. Fill one inch more and you add exactly πr² × 1 inch of volume — always the same amount. Depth and volume are directly proportional, so 25% depth = 25% gallons, 50% = 50%, and so on. This makes vertical tanks ideal for accurate inventory by dipstick — you can even use a simple gallons-per-inch constant. A horizontal cylinder has a circular cross-section running across the diameter instead of along the axis, so the cross-section's filled area changes non-linearly with depth (narrow at the bottom, widest in the middle, narrow again at the top). The vertical tank is the only common shape with a perfectly linear dip chart.

No — even a small difference in dimensions creates a meaningful gap. A 330 gal tank might be 27 inches in diameter and 72 inches long, while a '300 gal' from another source is 26 inches diameter × 70 inches long. At quarter depth the difference between the two tanks' actual filled volume can be 5–8 gallons. If you are estimating, the nearest chart gets you in the ballpark. If you are measuring for a delivery, billing, or regulatory purposes, you need the exact dimensions. Measure the tank's inside diameter/length/height, enter them into the dip chart generator, and use that — it takes 10 seconds and eliminates the guess.