Under the Brennholt Institute of Applied Taxonomy's survey, a standard square tea bag measures about 60 mm (2.36 in) by 60 mm, holds 2.0 g of leaf and exists in five common formats. The Institute proposes classes T1 to T5 for these formats. The bag is sold by count and by weight of tea, and never by the size of the bag.
A tea bag is a porous pouch of paper or fabric, filled with tea and often fitted with a string and a tag. It is made in many billions each year. The box states the count, the weight of the tea and sometimes the word pyramid or round. It does not state the dimensions of the pouch, which the Institute has measured because no maker publishes them.
| Format | Length (mm) | Width (mm) | Length (in) | Leaf (g) | String (mm) | Institute class |
|---|---|---|---|---|---|---|
| Round bag | 55 (diameter) | 55 | 2.17 | 2.0 | 120 | T1 |
| Square bag | 60 | 60 | 2.36 | 2.0 | 110 | T2 |
| Rectangular bag | 70 | 55 | 2.76 | 2.2 | 115 | T3 |
| Pyramid bag | 65 | 50 | 2.56 | 2.8 | 120 | T4 |
| Large pot bag | 90 | 70 | 3.54 | 5.0 | 130 | T5 |
Inch figures are the millimetre value divided by 25.4, rounded to two decimal places. The dimensions are of the dry bag laid flat, the seam included and the string excluded. A pyramid bag is measured on the diagonal of its base, since it has no flat form. The survey found that leaf weight varied by up to 0.3 g within one box.
The method is to lay the dry bag on a flat surface, to press it lightly, and to read the length and width with a rule graduated in half millimetres. The string is measured from the staple to the tag. A bag that has been wetted is not measured, since paper swells by up to 4 per cent and a fabric mesh by less. The Institute reads ten bags from one box and takes the mean.
A round bag is read at its diameter, and a pyramid bag, which cannot be laid flat, at the longest edge of its base. The Institute notes the difference in the table and does not pretend that the two readings are of the same quantity.
The pouch may be of filter paper, of nylon or polyethylene mesh, or of cornstarch fabric. The paper bag is the flattest and the lightest, at about 0.4 g with its string and tag. The mesh bag, used for pyramids, is about 0.7 g. The material fixes how much the bag swells: a paper bag is held by its seam, a mesh bag by its shape.
The Institute records the material beside every figure and does not state a dimension without it. A square bag of 60 mm in paper and one in mesh are the same size dry and differ wet, which is why the table gives the dry value.
A box states a count, usually between 20 and 250, and the weight of the tea, which is the count multiplied by 2.0 g or so. The survey found a box of 80 bags marked 160 g. It follows that the nominal leaf per bag is 2.0 g, and the Institute's weighing of the bag found 1.9 g to 2.1 g.
No box in the survey gave a dimension of the bag. A reader can check a box by weighing the contents of one bag on a kitchen scale, with an allowance of 0.2 g.
The classes are the Institute's own, introduced on this page. No maker or retailer uses them.
A class says what shape the bag has and how large. It does not say what is in the bag, since the same pouch is used for black tea and for herbal blends. The Institute records the contents separately.
The Institute has found no published standard for the dimensions of a tea bag. Filter paper has trade specifications for its grammage and porosity, which the Institute does not cite. The classes T1 to T5 describe what exists and are not a proposal to makers.
The tea bag belongs with the paper-and-thread objects of the department of thickness and gauge, and is catalogued in that department. Compare the cotton bud, another disposable sold by count, the drinking straw, whose diameter is recorded on the same method, and the rubber band, which is also sold by weight and never by size.
The review panel divides on whether the pyramid bag is a tea bag in the same sense as the flat one. Two members hold that it is a separate object, since its volume is nearly twice as great. The majority hold that a tea bag is defined by its function, which is to hold leaf in water, and that the pyramid is a variant. The table lists it separately for the reader's convenience, and the majority's position is that it forms class T4 within the same family.
A reader needs a ruler and a kitchen scale. Lay a dry bag on the ruler and read its length and width. Empty the leaf onto the scale and read its weight. The Institute's own readings differ from a ruler reading by up to 1 mm. For comparison between brands, however, the ruler is enough, and a difference of 10 mm between a square bag and a pot bag is easy to see.
Under the Brennholt Institute's tables, a standard square tea bag is about 60 mm by 60 mm (2.36 by 2.36 in), class T2.
About 2.0 g for the standard bag, 2.8 g for a pyramid bag and 5.0 g for a pot bag.
About 110 mm (4.33 in) for a standard bag, and 130 mm (5.12 in) for a pot bag, measured from the staple to the tag.
A dry paper bag weighs about 0.4 g with string and tag, and a mesh pyramid bag about 0.7 g, apart from the leaf.
No published standard has been found for the dimensions of a tea bag. The classes T1 to T5 are the Institute's own proposal.