Tank Strapping Chart Calculator
Pick your tank's shape, enter its dimensions, and generate a full depth-to-volume chart you can read a dipstick or gauge against — download it as CSV.
Worked examples
Farm diesel tank read off a dipstick
An operator strapping a flat-headed horizontal diesel tank so any driver can convert a stick reading to litres without guessing.
- D
- 2 m
- L
- 5 m
- step
- 0.2 m
A 0.4 m dip = 2,236 L, but 1.0 m = 7,854 L — the middle fills far faster
Upright water cistern with a wall gauge
A flat-bottomed vertical tank where volume rises evenly, so the chart is a straight line the gauge reads directly.
- D
- 2 m
- H
- 3 m
- step
- 0.5 m
Every 0.5 m adds a steady 1,571 L, up to 9,425 L full
Where a strapping chart is actually used
The chart this page builds is the same document, in miniature, as the one bolted to a bulk-storage tank or handed across at a custody-transfer inspection: a depth-to-volume table specific to one tank, kept so a buyer, a seller, and an inspector all read the same figure off the same dip. Petroleum terminals, chemical plants, and fuel distributors settle deliveries, tank-to-tank transfers, and monthly inventory reconciliations this way — by looking a dip up against a chart, not by re-deriving the geometry on the spot.
The standards family covering how those official charts get made is API MPMS Chapter 2, Tank Calibration — the American Petroleum Institute's Manual of Petroleum Measurement Standards methods for physically strapping or gauging a tank, documenting the resulting uncertainty, and issuing (and revising) a calibration table from that survey. A chart produced under API MPMS traces back to a real, physical measurement of that specific tank — a calibrated strapping tape run around the shell, or an optical/electro-optical reference method on larger vessels — not a set of nominal dimensions read off a fabrication drawing.
This calculator produces the other kind of chart: computed directly from the dimensions you enter, using exact closed-form geometry rather than a field survey. That makes it the right tool for sizing a new tank, replacing a lost chart on a shop or farm tank, or sanity-checking a supplier-issued table against the math — not a substitute for a certified strapping when money, custody, or an auditor is on the other end of the number. See reading a tank dip chart for the field corrections — tilt, sediment, temperature — that a real survey folds in and a calculated chart from nominal dimensions can't.
How a strapping chart is calculated
A strapping chart is just the tank's volume-vs-depth curve sampled at a fixed step. For each row the calculator takes the dip depth h and computes the liquid volume at that level using the same closed-form geometry a single-answer tank volume calculator uses — there's no lookup table or approximation. The only difference is that here it's evaluated once per increment, from empty to full, to build the whole table at once.
For a horizontal cylindrical shell the wetted cross-section at depth h is a circular segment, so the volume is that segment's area times the shell length L:
Dished, hemispherical, and custom heads add a capped-ellipsoid term on top of the straight section; an oval cross-section stretches the segment into an ellipse; and a vertical cone/frustum integrates a linearly tapering radius up to h. Because the horizontal-cylinder term is strongly non-linear — flat near the bottom and top, steep through the middle — the resulting chart is a curve, which is exactly why reading a dipstick against a proper table beats assuming volume is proportional to depth.
Worked example: a 5-point chart for a horizontal cylinder
Take a horizontal tank 4 ft in diameter (r = 2 ft) and 10 ft long — close to a common 1,000-gallon shop or farm fuel tank — flat heads, and generate a chart at a 1 ft increment. Five rows, empty to full, each one the segment-area formula above evaluated at that depth:
| Dip depth | Volume | Fill % |
|---|---|---|
| 0 ft | 0 gal | 0.0% |
| 1 ft | 183.8 gal | 19.6% |
| 2 ft | 470.0 gal | 50.0% |
| 3 ft | 756.3 gal | 80.4% |
| 4 ft | 940.0 gal | 100.0% |
The 2 ft row is worth checking by hand, not just by calculator: at exactly half the diameter, the liquid surface passes through the shell's centerline and splits the circular cross-section into two equal halves by plain symmetry, so that row has to land on exactly 50.0% regardless of who or what did the arithmetic. It's the fastest sanity check for a chart you didn't build yourself, calculated or field-strapped alike — if the mid-depth row isn't exactly half the total, something's wrong with the numbers or the geometry assumed, not with rounding. The segment-area formula itself is standard closed-form solid geometry, given in general references such as CRC Standard Mathematical Tables and Formulae, and it's the same shape tabulated as horizontal-tank partial-volume charts in petroleum-measurement handbooks alongside the API MPMS field methods above.
Enter these same numbers — 4 ft, 10 ft, flat heads, 1 ft step — into the calculator and it reproduces this table row for row, which is worth doing once as a trust exercise before relying on it for a real tank. For a single depth rather than a full table, the same figures check out against the tank volume calculator, or, ignoring the tank shell altogether, the plain cylinder volume calculator.
Limits: what a calculated chart won't catch
Head geometry is a choice, not a measurement. The five horizontal head options above — flat, 2:1 semi-elliptical, hemispherical, custom ellipsoidal, and oval cross-section — cover the shapes actually in use, but only if you pick the one that matches the tank in front of you. A torispherical (ASME flanged-and-dished) head, genuinely the most common shape on small-to-mid horizontal tanks, bulges out somewhere between a flat and a 2:1 elliptical head; approximating it with either built-in option is usually within a percent or two of true, but it is an approximation — and on a short, fat tank where the heads are a large share of total volume, that choice is the biggest source of error in the whole chart, bigger than any depth-reading precision you'll ever get from a stick.
Every row assumes the tank is level. The segment formula treats the liquid surface as a perfect horizontal plane, square to the tank's axis. Real horizontal tanks are routinely installed with a slight intentional slope toward the outlet, and settle further out of level over years on soil or a wooden cradle. A tank tilted even a degree or two puts the dip point measurably off the tank's true average depth — and because the segment curve is steepest through the middle, that error is largest exactly at the half-full readings a tank spends most of its life at. A calculated chart has no way to know about or correct for that; only a field strapping survey measures the tank as it actually sits.
Both limits point the same direction: this chart is exact geometry for an idealized tank, not a stand-in for a certified calibration. For the mechanics of tilt, dished-end corrections, and the temperature (VCF) adjustment custody-transfer readings also need, see reading a tank dip chart — and for a step-by-step walkthrough of producing a chart like the one above starting from a bare tank and a strapping tape, the companion guide on building a strapping chart from scratch covers the field-measurement side this calculator doesn't.
Frequently asked questions
What is a tank strapping chart, and why is it not just a straight line?
A strapping chart (also called a tank chart, dip chart, or gauge table) lists the liquid volume in a tank at each dip depth, so anyone reading a dipstick or sight gauge can convert a height straight to gallons or litres. For a vertical flat-bottomed tank the chart really is a straight line — volume rises evenly with depth. But a horizontal cylinder fills fastest through the middle and slowest near the very bottom and top, because each inch of depth exposes a wider or narrower circular slice. That curvature is exactly why a printed chart exists: you can't eyeball the numbers, so the tank is 'strapped' once and the table is trusted from then on.
How was the original chart on my tank measured — and can this replace it?
Traditionally a tank was strapped by physically measuring its circumference and dimensions with a strapping tape (hence the name) and computing volume per increment. This calculator reproduces the same result from the tank's stated dimensions using exact geometry, which is ideal for a new tank, a lost chart, or a quick cross-check. For custody-transfer or legal-for-trade metering, a certified field strapping is still the official record — treat this chart as an accurate working reference rather than a calibrated certificate.
Does this chart meet API MPMS requirements for custody transfer?
No, and it isn't meant to. API MPMS Chapter 2 (Tank Calibration) sets out the field procedures — physical strapping-tape measurement or an optical reference method, plus documented uncertainty and revision control — that produce a tank's official, auditable capacity table. This calculator instead computes an idealized chart from the dimensions you enter, the same shortcut engineers use for sizing, dosing, and quick cross-checks. It's the right tool for a farm tank, a shop cistern, or a fast sanity check on a supplier's numbers; for a custody-transfer meter, a terminal delivery ticket, or anything an auditor will pull up, the chart of record has to come from an actual field calibration performed and certified to that standard.
Which increment should I choose for the depth column?
Match it to how finely you actually read the tank. A dipstick marked in inches wants a 1-inch increment; a wall gauge you read to the centimetre wants a 1-cm (or a round 25/50-mm) step. Finer increments give a longer, more precise table but more rows to scan, so most field charts settle on 1 in, 1 cm, or 2 cm. You can regenerate the chart at a different increment any time without re-entering the tank.
Why doesn't the volume at the halfway depth equal half the tank?
On a horizontal cylinder it does, by symmetry — the halfway depth is exactly 50%. But add dished or hemispherical heads, an oval cross-section, or a cone bottom and the symmetry breaks: a cone-bottom tank, for instance, holds very little near its narrow base, so its halfway depth sits well under 50% of capacity. The chart accounts for every one of these shapes directly, which is the whole reason a per-depth table beats a single 'percent full' rule of thumb.
Can I use this chart for fuel, heating oil, water, or chemical tanks?
Yes — the chart is pure geometry, so it applies to any liquid: diesel and gasoline farm tanks, home heating-oil tanks, water and rainwater cisterns, and process or chemical storage. It reports the physical volume at each depth; it does not apply a temperature correction for fuels (volume-correction factors for gasoline or diesel are a separate step your metering standard may require), so for temperature-sensitive custody metering, apply your VCF to these figures afterward.
Where should I measure the dip depth from?
Always from the lowest interior point the liquid can reach, straight up to the surface. For a horizontal tank that's the very bottom of the round shell, not the top of the saddles or legs it rests on; for a cone-bottom or sphere-bottom vertical tank it's the tip of the cone or the bottom of the sphere. The chart's 0 row corresponds to that lowest point, so line your dipstick's zero up with the same spot.