550 gallon oil tank chart
A 550 gallon heating oil tank is a steel cylinder lying on its side, about 48 in across and 72 in long. PickHVAC's size chart lists it as "72”x48”" and says "550G tanks are filled to about 500 gallons". The same page says most are set above ground outside. You dip it from the top, so the stick reads the depth of oil at the middle, and the table below turns each inch into gallons.
Your reading
That is the geometric volume of a 48 in round, 72 in long cylinder, in cubic inches divided by 231. A tank is never filled to the brim, so the oil you can have in it is lower (see "How full a delivery fills it").
Why the chart is not linear
On a round tank the same inch of stick holds different amounts at different heights. The first 6 in of depth hold 41 gal, the 6 in around the middle hold about 90 gal, and the top 6 in hold only 41 gal. At 24 in the tank is exactly half full (282 gal). Near the middle one inch is worth about 15.0 gal, so a half inch error on the stick moves the answer by roughly 8 gal.
Float gauge marks in gallons
The gauge on the fill pipe shows F, ¾, ½, ¼. This table gives the gallons at each mark and the dip to the nearest half inch, using the full volume above. Because the tank is round, the ¼ mark sits at 14.5 in on the stick, which is more than a quarter of the 48 in.
| Gauge | Gallons | Dip |
|---|---|---|
| Full | 564 | 48.0 in |
| 3/4 | 423 | 33.5 in |
| 1/2 | 282 | 24.0 in |
| 1/4 | 141 | 14.5 in |
| 1/8 | 71 | 8.5 in |
Inches to gallons
| Dip | Gallons | Full |
|---|---|---|
| 0 in | 0.0 | 0.0% |
| 1 in | 2.9 | 0.5% |
| 2 in | 8.0 | 1.4% |
| 3 in | 14.7 | 2.6% |
| 4 in | 22.4 | 4.0% |
| 5 in | 31.2 | 5.5% |
| 6 in | 40.7 | 7.2% |
| 7 in | 50.9 | 9.0% |
| 8 in | 61.8 | 11.0% |
| 9 in | 73.2 | 13.0% |
| 10 in | 85.1 | 15.1% |
| 11 in | 97.5 | 17.3% |
| 12 in | 110.3 | 19.6% |
| 13 in | 123.4 | 21.9% |
| 14 in | 136.8 | 24.3% |
| 15 in | 150.6 | 26.7% |
| 16 in | 164.6 | 29.2% |
| 17 in | 178.8 | 31.7% |
| 18 in | 193.2 | 34.3% |
| 19 in | 207.7 | 36.8% |
| 20 in | 222.4 | 39.4% |
| 21 in | 237.2 | 42.1% |
| 22 in | 252.1 | 44.7% |
| 23 in | 267.1 | 47.3% |
| 24 in | 282.0 | 50.0% |
| 25 in | 297.0 | 52.7% |
| 26 in | 311.9 | 55.3% |
| 27 in | 326.8 | 57.9% |
| 28 in | 341.6 | 60.6% |
| 29 in | 356.3 | 63.2% |
| 30 in | 370.8 | 65.7% |
| 31 in | 385.2 | 68.3% |
| 32 in | 399.4 | 70.8% |
| 33 in | 413.4 | 73.3% |
| 34 in | 427.2 | 75.7% |
| 35 in | 440.6 | 78.1% |
| 36 in | 453.8 | 80.4% |
| 37 in | 466.5 | 82.7% |
| 38 in | 478.9 | 84.9% |
| 39 in | 490.8 | 87.0% |
| 40 in | 502.2 | 89.0% |
| 41 in | 513.1 | 91.0% |
| 42 in | 523.3 | 92.8% |
| 43 in | 532.9 | 94.5% |
| 44 in | 541.6 | 96.0% |
| 45 in | 549.3 | 97.4% |
| 46 in | 556.0 | 98.6% |
| 47 in | 561.2 | 99.5% |
| 48 in | 564.0 | 100.0% |
How full a delivery fills it
A 550 is sold by its label, and the oil it holds is less. PickHVAC's chart page lists a maximum fill of "468 to 495 gallons" for a 550 at 85% to 90%, and notes that 90% is the average maximum. TankVolume gives about 500 gallons as the typical fill. By my table, a stick reading of 40.0 in is 502 gal, which is where a 500 gallon fill lands. A stick that reads 42 in (523 gal) means the tank is close to the top and a delivery has little room.
The sizes differ between charts
Chart sources do not agree on how big a 550 is. The two above use 48 x 72 in. TankVolume calls its 48 in diameter and 72 in length "representative values only" and warns that "Other supplier charts may use different dimensions". Other suppliers may list different sizes. A tank that is a different size has a different table, so measure the diameter and the length of yours, or read the label on the tank, before trusting any chart. The calculator takes custom sizes.
Worked example: when to call
A stick reading of 12 in is 110 gal (20% of the full volume). I keep a reserve of 10% (56 gal) in the numbers, which is my own choice. That leaves 54 gal. A large house burning 5 gal a day (an example) has 10 days. Your rate comes from two dips a week or two apart, and the run-out guide shows how. The calculator does the sums with the 550 preset and a 12 in reading already filled in.
Smaller tanks: the 330 gallon chart and the 275 gallon chart cover the oval tanks. For dollars, see the cost to fill a tank.