We checked 406 tanks against their makers' own documents

1. A tank holds less than its outside size. Median 86% of the outside cylinder, across 228 round tanks from Sintex, Vectus and Norwesco.
2. Some printed sizes cannot hold the rated capacity. The Vectus 10,000 L tank is printed as 2045 × 2800 mm. That outside cylinder encloses only 9,197 L. Vectus states that its sizes are approximate.
3. A brochure contradicts itself. 8 rows in the Sintex brochure print a millimetre value and an inch value that do not agree.
4. Drawings and web tables disagree. All five Norwesco drawings that we checked give a different height from the web table.
5. Charts and geometry differ. Granby's 275 gal vertical chart is 2.1% above the geometry of its printed size, on average.
6. Charts and formulas differ. Amtrol's quick expansion-tank chart picks a different tank from Amtrol's own formula in 8 of 45 cells.

These issues change the number that you get when you measure a tank or read a chart. Each one is described below, with its source.

For every round tank, we divided the rated capacity by the volume of a plain cylinder with the printed outside diameter and overall height. A result of 100% means the outside cylinder holds exactly the rating. The real tank is always smaller than its outside cylinder, so a value near or above 100% is suspect.

The median for all 228 tanks is 86%. Norwesco tanks are higher (90%) than Sintex overhead tanks (83%). Sintex underground sumps are the lowest (71%). Their printed height can include the manhole neck.

Use this as a rule. If you calculate a volume from a tape around the outside of a poly tank, multiply it by about 0.8 to 0.9 (about 0.7 for an underground sump). Better, measure the inside, or use the maker's moulded marks.

Two outliers. The Vectus 10,000 L (2045 × 2800 mm) encloses only 9,197 L, which is 92% of its rating. Vectus states that all its sizes are approximate. The Norwesco 1,050 gal vertical tank (48 × 134 in) encloses 1,050 gal: the outside cylinder is the same as the rating, with no space for the wall.

The Sintex brochure prints every size in millimetres and in inches. In most rows the two agree. In these rows they do not:

• Sintex Reno 1000 L: hatch printed as 406 mm and 15.75 in (400 mm).
• Sintex Reno 1500 L: height printed as 1155 mm and 45.17 in (1147 mm); hatch printed as 400 mm and 15.98 in (406 mm).
• Sintex Reno 2000 L: hatch printed as 407 mm and 15.75 in (400 mm).
• Sintex Reno 2500 L: hatch printed as 400 mm and 16.02 in (407 mm).
• Sintex Loft 425 L: height printed as 407 mm and 17.13 in (435 mm).
• Sintex Loft 460 L: height printed as 325 mm and 16.02 in (407 mm).
• Sintex Loft 475 L: height printed as 435 mm and 12.8 in (325 mm); length printed as 1585 mm and 52.4 in (1331 mm).
• Sintex Loft 500 L: height printed as 510 mm and 17.13 in (435 mm).

For the 460 L loft tank, the printed 325 mm height gives an outside box of only 459 L. The inch value (16.02 in, 407 mm) is consistent with the capacity. The Sintex Hero 3000 L height is printed as “78..54” in. These rows are marked on our Sintex pages.

Other makers: Manchester prints 3875.4 litres for its 1000 gal tank (1000 US gal is 3785.4 L). Roth prints a shipping weight of 258 lb for the DWT 1500L, which is less than its tank weight of 333 lb. Chem-Tainer's 2025 catalog prints a 61 gal rectangular tank as 36 × 36 × 36 in, the same size as its 185 gal tank. A box of that size holds about 202 gal. It also prints a 90 gal tank as 24 × 36 × 12 in (about 45 gal as a box) and a 2,635 gal elliptical tank whose printed size encloses only about 2,217 gal. These rows are marked on our Chem-Tainer page.

The web table and the 2024 catalog agree with each other. Only the drawings differ. Snyder's 1500 gal tank has a 65 in diameter in the web table and Ø64.0 in on the drawing. The same drawing names the shell “1500V X 65 RP” and states: “ALL DIMENSIONS ON ROTATIONAL MOLDED PARTS ARE SUBJECT TO A ± 3% TOLERANCE.” The difference is within that tolerance. Manchester's 1000 gal tank has an overall length of 15 ft 8½ in on the sheet dated 4/11/2025 and 15 ft 11 in on a spec sheet created in December 2024. Manchester states that all vessel dimensions are approximate.

Granby publishes a capacity chart for its vertical tanks. We compared the 275 gal column with the geometry of the printed size (27 × 44 × 60 in, flat sides with round ends). From 4 in upward, the chart is -0.3% to +2.3% above the geometry, +2.1% on average. At 44 in, the chart gives 273.8 gal and the geometry gives 267.9 gal. This is close to the precision that Granby prints on the chart: “PRECISION IS ABOUT +/- 2%”. One possible reason is that the printed size is nominal. Granby's generic drawings, which cover several models, include callouts such as 44¼ and 27¼ in. At the printed size, the geometry at full height is 267.9 gal, which is below the 275 gal rating.

On Granby's product page, the link labelled “Capacity Chart for US Horizontal Tanks” opens the vertical chart. We found no horizontal chart. In Roth's fill chart, two cells of the 1000L column break the sequence: 125 gal at 30 in (between 132 and 140) and 56 L at 32 in (between 530 and 575).

Amtrol publishes a formula for thermal expansion tanks and a quick sizing chart. In 8 of the 45 chart cells, the chart picks a different tank from the formula. For example, at 50 gal, 160 °F and 40 psi, the formula gives 1.05 gal of expanded water, which is more than the 0.9 gal that the chart's ST-5 accepts. In 7 of the 8 cells, the chart picks the larger tank, so it is the more conservative choice. In two of them the values are an exact tie. Our expansion tank calculator shows both and recommends the larger tank.

1. We used only the makers' own documents: brochures, catalogs, product pages, drawings and charts. We did not use retailer listings.
2. We copied every value as printed. Where a document has no text layer, we used OCR and then checked each row against the printed millimetre and inch pair and against the page image.
3. A second reviewer checked all 115 Sintex rows and all 167 Chem-Tainer rows against the page images.
4. We calculated geometry with the same engine as our calculators. Its accuracy is described on the methodology page.
5. We recorded every disagreement as printed. We did not correct a maker's value.

All documents were retrieved and checked on 1 November 2026. Makers change their documents, so a later edition can differ.

1. Read the label, the nameplate or the part number first. It identifies the tank better than a tape.
2. Measure the outside diameter and the overall height. Use find my tank to match the model.
3. Do not use the outside cylinder as the capacity. Multiply it by about 0.8 to 0.9, or measure the inside.
4. Use the maker's chart if one is published, and check it against a delivery ticket.
5. If two of the maker's documents disagree, use the newer one, and ask the maker.

tank-maker-dimensions-2026-11.csv lists all 406 tanks: maker, model, capacity, shape, printed outside sizes in millimetres, and the page on this site (or, for Vectus, the maker's page) with the source. Please cite tankvolumecalc.com and the maker's document when you use it.

tankvolumecalc.com is not affiliated with any maker named here. All figures are as the makers print them.

Sources and standards

1. Sintex WST Brochure 2026 (March)Sintex-BAPL Limited (Welspun) — manufacturerhttps://www.sintexonline.com/wp-content/uploads/2025/03/Sintex-WST-Brochure_2026-March-1.pdf
2. Vectus ISI Tank — product page specification tableVectus Industries — manufacturerhttps://www.vectus.in/water-storage-tanks/overhead-tanks/vectus-isi-tank
3. Norwesco Liquid Storage Tanks catalog (LSTcatalog2024-1.pdf)Norwesco, Inc. — manufacturerhttps://www.norwesco.com/_site_components/uploads/pdfs/catalogs/LSTcatalog2024-1.pdf
4. Chem-Tainer 2025 CatalogChem-Tainer Industries, Inc. — manufacturerhttps://chemtainer.com/wp-content/uploads/2025/08/ChemTainer_2025Catalog_082525.pdf
5. Granby capacity chart for vertical tanks (USA, v1)Granby Industries — manufacturerhttps://www.granbyindustries.com/app/uploads/2026/04/GranbyInd_Capacity-Chart_VerticalTanks_USA_v1.pdf
6. Roth EcoDWT plus 3 Fill ChartRoth North America — manufacturerhttps://www.roth-america.com/app/uploads/2022/03/DWT-Fill-Chart.pdf
7. Model pages with every other maker document (Norwesco, Snyder and Manchester drawings and sheets)tankvolumecalc.com registryhttps://tankvolumecalc.com/tanks/
8. Amtrol expansion tank sizing (formula and quick chart), as cited on the expansion tank pageAmtrol — manufacturerhttps://tankvolumecalc.com/expansion-tank-sizing/

Every linked source above was retrieved and checked on 2026-11-01.