Bag quotes are often requested with only a brief description such as “30 × 40, 50 microns”. Without further details, two suppliers’ prices may not refer to the same product. This guide explains how to work out bag dimensions from your product and compare thickness, weight and price per kilogram.
How should bag dimensions be stated?
Bag dimensions are stated in centimetres as width × length. The width is the opening of the bag; the length is the distance from the opening to the base. Details that are not included in these dimensions but affect the bag should be specified separately:
- Gusset: An allowance folded inwards at the sides or base. For a gusseted bag, state the gusset depth separately.
- Flap allowance: The extra length that closes the opening on a bag with an adhesive strip or flap.
- Handle and grip: Vest handles, die-cut handles or reinforced handles affect the usable length of the bag.
From product dimensions to bag dimensions
A flat bag “loses” space in both width and length equal to the thickness of the product inside it. So add the product’s height to both the width and length. Allow a little extra for easy loading; for a bag with a flap, add the flap allowance to the length as well.
- Bag width ≈ product width + product height + loading allowance
- Bag length ≈ product length + product height + loading allowance (+ flap allowance)
Illustrative example: Figures are for showing the calculation only.
| Step | Example: folded T-shirt |
|---|---|
| Product dimensions (width × length × height) | 25 × 30 × 3 cm |
| Bag width | 25 + 3 + 2 = 30 cm |
| Bag length | 30 + 3 + 2 = 35 cm |
| Flap allowance for a bag with a flap | + 4 cm |
| Dimensions to state in the quote | 30 × 35 cm + 4 cm flap |
As product height increases, a gusseted bag will sit better than a flat bag. For a gusseted bag, the gusset depth is usually selected to be about the same as the product height, and the width is reduced accordingly. Always check the final dimensions with the actual product, preferably using a sample bag.
Thickness: what does micron mean?
Bag thickness is expressed in microns (µm); one micron is one thousandth of a millimetre. A 50-micron film is 0.05 mm thick. Clarify whether the quoted thickness is for one layer (one side of the bag) or the total thickness of both sides. The same bag may be described as “50 microns” in one quote and “100 microns, double layer” in another.
The required thickness depends on the weight being carried, the product’s corners, and whether the bag will be used by hand or for courier delivery. The production ranges for our product groups are:
| Product | Production thickness range |
|---|---|
| HDPE crinkle bags | 3–30 µm |
| Printed plastic bags | 8–80 µm |
| Courier mailer and handle bags | 100–200 µm |
These ranges indicate production options; they do not guarantee suitability for a particular product. Choose the appropriate thickness by testing it with the actual product.
Bag weight and number per kilogram
Bags are often sold by the kilogram, while you use them by the piece. To compare two quotes, calculate the weight of one bag. A flat bag has two sides, so the calculation is:
Bag weight (g) ≈ width (cm) × length (cm) × 2 × thickness (µm) × density (g/cm³) ÷ 10 000
Polyethylene has a density of approximately 0.92–0.96 g/cm³; soft PE bags are closer to the lower value, while crinkle bags are closer to the higher value.
Illustrative example: Uses hypothetical values; this is not a measurement of a Mertan product.
| Step | Example |
|---|---|
| Dimensions and thickness | 30 × 40 cm, 50 µm (single layer) |
| Assumed density | 0.92 g/cm³ |
| Weight of one bag | 30 × 40 × 2 × 50 × 0.92 ÷ 10 000 ≈ 11 g |
| Bags per kilogram | 1000 ÷ 11 ≈ 90 bags |
| If the hypothetical price per kilogram is 100 | Approximately 1.1 per bag |
This calculation excludes gussets, handles, flaps, printing ink and cutting waste; an actual bag may weigh slightly more or less. It is still enough to check whether two quotes describe the same bag. A quote with a lower price per kilogram but greater thickness may work out more expensive per bag.
Crinkle or soft PE?
A crinkle bag is thin and lightweight, and rustles when handled; it is economical for inner packaging and retail display use because it uses little material. A soft PE bag is more flexible and transparent, making it a good choice when product visibility and a soft feel matter. Find more detail on the difference between the two options for textile inner packaging in our towel and bathrobe packaging guide.
Checklist before requesting a quote
- The product’s width, length and height; dimensions for each item if there is more than one.
- Bag style: flat, gusseted, vest, die-cut handle or flap.
- Required thickness and whether this is single or double layer.
- Colour and printing requirements.
- Monthly usage: number of bags or kilograms.
- A photo or sample of the bag you currently use, if available.
Mertan Ambalaj manufactures bags to order in Denizli; there is no minimum order quantity. Send your dimensions using the quote form; for e-commerce shipments, you can also read our guide to choosing courier mailer bags.