Measure the oil in your tank with a stick or read the gauge, pick your tank, and get the gallons you have left. Charts for the standard 275, 330, 500, 550 and 1000 gallon tanks are below the calculator.
How to use it
Unscrew the fill cap (on a basement tank it is the larger pipe; on a buried tank it is the cap in the yard), lower a clean stick until it touches the bottom, and read where the oil wet the wood. Enter that number of inches. If you only have the float gauge on top of the tank, switch to Gauge and pick the mark the float points to.
The tank list covers the sizes that make up nearly every residential tank: the 275 and 330 gallon steel ovals that sit in basements and beside houses, and the 500, 550 and 1000 gallon steel cylinders that are usually buried. If your tank is a different cylinder, choose Other horizontal cylinder and enter its diameter and length.
Which tank do I have?
Get a tape measure. A 275 and a 330 have the same oval end, 27 by 44 inches. Length tells them apart: 60 inches for a 275, 72 inches for a 330. Then look at which way the oval stands. If it is 44 inches tall it is a vertical tank and the stick reads up to 44 inches. If it is 27 inches tall it is a horizontal tank and the stick only reads up to 27 inches. Mixing these two up is the most common reason a chart "doesn't match" a delivery. The data plate on the end of the tank, or an old delivery slip, usually confirms the size.
Buried tanks are harder because you can't see them. Most residential buried steel tanks are 48 inches in diameter, so a full stick reading near 48 inches suggests one of the 500, 550 or 1000 gallon cylinders. Your oil company's records are the best way to tell which one.
How the numbers are calculated
For the 275 and 330 gallon vertical tanks the calculator uses Granby Industries' published capacity chart for its standard UL-80 tanks, inch by inch, and interpolates between whole inches. Granby states the chart is accurate to about ±2%.
For the horizontal 275 and 330 the calculator works out the area of oil in the oval end and multiplies by the tank length. The oval is a rectangle with a half circle on each side:
Oil area (horizontal oval) = (44 − 27) × h + circle segment(r = 13.5, depth h)
circle segment = r² × acos((r − h) / r) − (r − h) × √(2rh − h²)
Gallons = area × length ÷ 231 × 1.022
The 1.022 factor accounts for the slightly domed ends. It is the ratio between Granby's charted full volume for the 275 vertical (273.8 gallons) and the plain geometry of a 27 × 44 × 60 inch oval. With that factor the same geometry reproduces Granby's vertical chart to within half a gallon at every inch, which is a good check that it is right for the horizontal tanks too.
The 550 and 1000 gallon sizes use Modern Welding's published nominal dimensions (48" × 6 ft for 550; 48" × 11 ft or 64" × 6 ft for 1000). For the 500 gallon size we used a 48-inch diameter and a 64-inch length, the length a 48-inch cylinder needs to hold 500 gallons. Buried tanks vary more by maker than basement tanks, so if your tank plate gives different dimensions, use Other horizontal cylinder.
Reading the result sensibly
A tank's rating is its full volume, but you can never use all of it. The supply line draws from a little above the bottom, and running a tank very low can pull sludge and water into the filter. Most oil dealers suggest ordering when you are down to about a quarter tank. At the top, the driver stops when the vent whistle goes quiet, so a "full" 275 normally holds about 220 to 250 gallons. The room in tank figure above is the space up to the chart's full mark, so expect a real delivery to be somewhat smaller.
Once you know your gallons, the days-left calculator turns them into a date to call your supplier.
Oil tank charts by size
Every row is computed with the method above. Open the chart for your tank, or print this page; the calculator and menus are hidden when printing.
275 gallon vertical oil tank chart (1–44 in)
Inches
Gallons
1
1.8
2
5.0
3
9.0
4
13.7
5
19.0
6
25.1
7
31.3
8
37.7
9
44.3
10
51.2
11
58.2
12
65.3
Inches
Gallons
13
72.4
14
79.6
15
86.7
16
93.9
17
101.1
18
108.2
19
115.4
20
122.6
21
129.7
22
136.9
23
144.1
24
151.2
Inches
Gallons
25
158.4
26
165.6
27
172.7
28
179.9
29
187.1
30
194.3
31
201.4
32
208.6
33
215.6
34
222.6
35
229.5
36
236.1
Inches
Gallons
37
242.6
38
248.7
39
254.4
40
259.8
41
264.6
42
268.7
43
272.0
44
273.8
275 gallon horizontal oil tank chart (1–27 in)
Inches
Gallons
1
6.3
2
14.1
3
22.8
4
32.1
5
41.9
6
52.2
7
62.9
8
73.8
9
85.0
10
96.3
11
107.8
12
119.4
Inches
Gallons
13
131.1
14
142.7
15
154.4
16
166.0
17
177.5
18
188.8
19
200.0
20
210.9
21
221.6
22
231.9
23
241.7
24
251.0
Inches
Gallons
25
259.7
26
267.5
27
273.8
330 gallon vertical oil tank chart (1–44 in)
Inches
Gallons
1
2.1
2
6.0
3
10.8
4
16.5
5
22.8
6
30.2
7
37.5
8
45.2
9
53.2
10
61.4
11
69.8
12
78.3
Inches
Gallons
13
86.9
14
95.5
15
104.1
16
112.7
17
121.3
18
129.9
19
138.5
20
147.1
21
155.7
22
164.3
23
172.9
24
181.5
Inches
Gallons
25
190.1
26
198.7
27
207.3
28
215.9
29
224.5
30
233.1
31
241.7
32
250.3
33
258.8
34
267.2
35
275.4
36
283.4
Inches
Gallons
37
291.1
38
298.4
39
305.3
40
311.7
41
317.5
42
322.5
43
326.4
44
328.6
330 gallon horizontal oil tank chart (1–27 in)
Inches
Gallons
1
7.6
2
16.9
3
27.3
4
38.5
5
50.3
6
62.7
7
75.4
8
88.5
9
101.9
10
115.6
11
129.4
12
143.3
Inches
Gallons
13
157.3
14
171.3
15
185.3
16
199.2
17
213.0
18
226.6
19
240.0
20
253.1
21
265.9
22
278.2
23
290.1
24
301.2
Inches
Gallons
25
311.6
26
321.0
27
328.6
500 gallon cylinder chart, 48" diameter (1–48 in)
Inches
Gallons
1
2.5
2
7.1
3
13.0
4
20.0
5
27.7
6
36.2
7
45.3
8
54.9
9
65.1
10
75.7
11
86.7
12
98.0
Inches
Gallons
13
109.7
14
121.6
15
133.9
16
146.3
17
158.9
18
171.7
19
184.7
20
197.7
21
210.9
22
224.1
23
237.4
24
250.7
Inches
Gallons
25
264.0
26
277.2
27
290.5
28
303.6
29
316.7
30
329.6
31
342.4
32
355.1
33
367.5
34
379.7
35
391.7
36
403.3
Inches
Gallons
37
414.7
38
425.7
39
436.3
40
446.4
41
456.1
42
465.2
43
473.6
44
481.4
45
488.3
46
494.2
47
498.8
48
501.3
550 gallon cylinder chart, 48" × 72" (1–48 in)
Inches
Gallons
1
2.9
2
8.0
3
14.7
4
22.4
5
31.2
6
40.7
7
50.9
8
61.8
9
73.2
10
85.1
11
97.5
12
110.3
Inches
Gallons
13
123.4
14
136.8
15
150.6
16
164.6
17
178.8
18
193.2
19
207.7
20
222.4
21
237.2
22
252.1
23
267.1
24
282.0
Inches
Gallons
25
297.0
26
311.9
27
326.8
28
341.6
29
356.3
30
370.8
31
385.2
32
399.4
33
413.4
34
427.2
35
440.6
36
453.8
Inches
Gallons
37
466.5
38
478.9
39
490.8
40
502.2
41
513.1
42
523.3
43
532.9
44
541.6
45
549.3
46
556.0
47
561.2
48
564.0
1000 gallon cylinder chart, 48" × 132" (1–48 in)
Inches
Gallons
1
5.2
2
14.7
3
26.9
4
41.2
5
57.1
6
74.6
7
93.4
8
113.3
9
134.2
10
156.1
11
178.7
12
202.2
Inches
Gallons
13
226.2
14
250.9
15
276.1
16
301.7
17
327.8
18
354.2
19
380.9
20
407.8
21
434.9
22
462.2
23
489.6
24
517.0
Inches
Gallons
25
544.4
26
571.8
27
599.1
28
626.2
29
653.2
30
679.9
31
706.3
32
732.3
33
758.0
34
783.1
35
807.8
36
831.9
Inches
Gallons
37
855.3
38
878.0
39
899.8
40
920.8
41
940.7
42
959.4
43
976.9
44
992.9
45
1007.1
46
1019.3
47
1028.8
48
1034.0
1000 gallon cylinder chart, 64" × 72" (1–64 in)
Inches
Gallons
1
3.3
2
9.3
3
17.0
4
26.1
5
36.3
6
47.5
7
59.5
8
72.3
9
85.9
10
100.1
11
114.8
12
130.1
Inches
Gallons
13
146.0
14
162.2
15
178.9
16
196.0
17
213.5
18
231.3
19
249.3
20
267.7
21
286.3
22
305.2
23
324.2
24
343.4
Inches
Gallons
25
362.8
26
382.4
27
402.0
28
421.8
29
441.6
30
461.5
31
481.4
32
501.3
33
521.3
34
541.2
35
561.1
36
580.9
Inches
Gallons
37
600.7
38
620.3
39
639.9
40
659.3
41
678.5
42
697.5
43
716.4
44
735.0
45
753.4
46
771.4
47
789.2
48
806.7
Inches
Gallons
49
823.8
50
840.5
51
856.7
52
872.5
53
887.9
54
902.6
55
916.8
56
930.4
57
943.2
58
955.2
59
966.4
60
976.6
Inches
Gallons
61
985.7
62
993.4
63
999.4
64
1002.7
Cylinder charts are pure geometry, so their full figure can land slightly above the nominal size (for example 564 gallons for a 48" × 72" "550").
Frequently asked questions
How many gallons are in a 275 gallon oil tank at 20 inches?
In a vertical 275 (standing 44 inches tall) 20 inches is about 123 gallons, according to Granby's published capacity chart. In a horizontal 275 (lying on its side, 27 inches tall) 20 inches is about 211 gallons, because the stick scale is shorter and each inch holds more oil.
How do I know if my 275 tank is vertical or horizontal?
Measure the height of the tank body, not counting the legs. About 44 inches tall and 27 inches deep means vertical. About 27 inches tall and 44 inches deep means horizontal. Both are 60 inches long.
Why does a 275 gallon tank only take about 220 to 240 gallons?
The rating is the tank's total volume. Drivers stop when the vent alarm stops whistling, which leaves expansion room at the top, and you rarely let the tank run completely empty. A delivery of 200 to 240 gallons into a 275 is normal.
Is the gauge on top of my tank accurate?
Float gauges are a rough guide. They can stick, and the 1/4, 1/2, 3/4 marks are usually spread evenly over the tank height rather than being matched to its exact shape. A measuring stick through the fill pipe, read against the right chart, is more reliable.
How do I stick a buried oil tank?
Lower a clean wooden stick (or a stick marked in inches) straight down the fill pipe until it touches bottom, pull it up and read the wet line. Water-finding paste on the tip shows whether there is water at the bottom. Do not dig around a buried tank yourself.