How to Write a Bag Pattern and Grading Sheet

A bag pack usually stops at the drawing: a dimensioned sketch, a materials list and a construction note. What the cut room actually works from is a set of flat shapes, one per panel, each carrying a seam allowance and a direction. Where the pack stops at the drawing, the cut room makes the pattern, and the pattern it makes is not written down anywhere.

That is tolerable on one size and expensive on three. The moment a programme runs more than one size, or the moment a second run is ordered, an unwritten pattern becomes a re-drawing exercise, and a re-drawn panel is the most common cause of a second run that does not match the first.

The two documents that close this are short. A pattern piece list is a table of a dozen rows. A grading sheet is a table with one column per size. Neither is a design artefact, and neither takes long to write, which is why their absence is harder to explain than their cost.

What Is a Pattern and How Does It Differ From a Tech Pack?

A pattern is the flat shape of each panel, at full size, including the seam allowance. It is what the cutter lays on the cloth and what the marker is built from. A tech pack describes the bag; a pattern is the bag, reduced to shapes that can be cut and sewn in a sequence.

The distinction matters because a drawing can be fully dimensioned and still not be cuttable. A dimension on a sketch is a measurement of the finished bag; a pattern piece is the shape that produces that measurement after the seam allowance is folded and sewn. The two differ by the seam allowance on every edge, and by the behaviour of the cloth on a curve.

In practice the pattern and the pack are made by different people at different times, which is why they drift. Holding the pattern piece list inside the pack, as a table of piece names with the material and the cut direction, is what keeps the two in step across a run.

What Goes on a Pattern Piece List?

One row per piece, and about eight fields. The piece name, because the same panel carries different names in different rooms. The quantity per bag, because a panel can be cut twice or four times. The material, because a lining piece and a shell piece of the same shape are not interchangeable. The cut direction, because a coated cloth and a woven cloth behave differently on the grain.

The remaining four fields are the ones that get dropped: the seam allowance on each edge, whether the piece is cut on a fold, whether it is mirrored or handed, and whether it carries a notch or a drill mark that positions something else. A piece list without those four is a list of shapes rather than a cutting instruction, and the cut room will fill the gaps by itself.

What Is a Grading Sheet and When Does a Bag Need One?

A table giving every dimension of the bag for every size in the run. It is what turns one pattern into three. Where a bag comes in one size, no grading sheet is needed and the pack can say so in one line; where a run carries a small, a medium and a large, the grading sheet is the document that says what changes between them and by how much.

Bags need one less often than garments, and that is exactly why it is missed. A garment is graded by a set of body measurements and a set of rules that are largely settled; a bag has no body, so there is no default rule, and the increments have to be written by the person who designed the product.

The other case that needs one is a size run expressed as capacity: a six-bottle carrier and a twelve-bottle carrier, or a two-compartment and a three-compartment kit bag. There the change is in the panel area and in the divider rather than in a strap length, and those are the runs where an unwritten grading rule produces a bag that holds the right number of items and does not close.

How Is a Bag Graded Differently From a Garment?

By proportion rather than by a body. A garment grade is driven by measurements that do not move much between brands; a bag grade is driven by what goes inside it, and every brand decides that for itself. There is no published rule for how much a cooler bag grows between a small and a medium, and there is no standard increment to fall back on.

The second difference is that a bag grade is uneven. A garment grows by a comparable amount at most points; a bag very often grows in one dimension only, while the strap, the hardware and every trim stay exactly the same. Writing which dimensions move and which are held is the whole of the work, and it is a shorter document than a garment grade for that reason.

The third is that the components do not grade. A buckle, a zipper in most constructions, a foam sheet and a woven label are the same part across every size in a run. A grading sheet that scales every line produces a BOM with three zipper lengths where one would do, three purchase orders where one would do, and three times the exposure to a minimum.

What Does Each Row on a Grading Sheet Carry?

The dimension, whether it grades or is held, and the increment. Three columns per size is the usual shape: the base size value, then the value at each other size, then a note on what the change does to the BOM. A row for a held dimension should say held rather than repeat the same number, because a held number that reads as a graded one gets graded by the next person who picks the sheet up.

Two more columns are worth the space: what the change does to the pattern piece, and what it does to the carton. A body panel that grows 40 mm changes the marker and the consumption; a bag that grows in three dimensions changes the carton count and the freight on a container. Both are money, and neither is visible on a grading sheet unless somebody writes it down.

How Are Seam Allowance and Cut Direction Written?

Seam allowance as a figure in millimetres on each edge rather than as one figure for the piece, because a bound internal seam and a turned external edge take different allowances. Where a piece has four edges and three allowances, the piece list says which edge gets which, and the pattern carries the same figures.

Cut direction is written as an arrow on the piece and as a field in the list. Two things set it: the grain of a woven cloth, and the nap or the direction of a printed pattern. A piece cut across the grain on a woven shell behaves differently at the seam, and a piece cut against the nap on a printed panel reads as a different colour under the same light.

Where the cloth is coated or laminated there is a third consideration, which is that two pieces cut in opposite directions can differ in how they lie after welding. On a welded construction the direction field is worth carrying even where the cloth has no visible grain at all.

How Does the Marker Affect Consumption and Cost?

A marker is the arrangement of the pattern pieces on the cloth for one lay, and the efficiency of that arrangement is the difference between the consumption the pack assumed and the consumption the cut room reports. On a soft bag with a dozen pieces, a well-nested marker and a poorly nested one differ by a meaningful percentage of cloth.

The pack cannot control the marker, but it can state the consumption it was quoted against, which is the number that makes a later difference visible. Where the BOM says 0.62 linear metres per bag and the cut room reports 0.68, the piece list and the grading sheet are the two documents that show which end the difference came from.

The third thing a marker does is set the waste. A narrow cloth and a wide panel produce an offcut that is either used on a smaller piece or thrown away, and a piece list that names every small piece in the bag is what lets the marker use the offcut rather than bin it.

What File Format Does a Pattern Travel In?

As a vector file at full scale, most commonly DXF or PLT out of a pattern system, with a PDF at the same scale for reading. A pattern sent as a drawing inside a page-layout file is a picture of a pattern rather than a pattern, and it has to be re-digitised before any cutter can use it.

Two fields belong with the file, and both are more often missing than present. The first is the unit: a DXF carries no unit of its own, so a file drawn in millimetres and read as inches produces a bag roughly twenty-five times too large, and that failure has consumed more than one sampling cycle on more than one programme.

The second is the version. A pattern revised after a fit sample and sent without a revision mark is the reason a cut room cuts a superseded shape. A version number on the file and the same revision letter on the piece list cost nothing and remove the failure entirely.

What Are the Common Errors on a Pattern and Grading Sheet?

Five recur. A piece list that omits the quantity per bag. A grading sheet that scales a component rather than holding it. A seam allowance stated once for a piece with three different edges. A cut direction that is drawn on the piece and never written in the list. And a pattern file sent without a unit, which is the one that costs a full sampling cycle rather than a correction.

The sixth is not an error in the document but an error around it: a pattern that is never returned. Where a programme pays for development and the cut file stays with the cut room, a second run is a re-development, and the quote for that second run is a quote for work that was already paid for once. Asking for the file is a one-line request and it is worth making at the start.

How Do the Pattern and the Grading Sheet Reach the BOM?

Through the consumption line. Each piece contributes an area, the areas are nested into a marker, and the marker gives a length of cloth per bag at a stated width. The grading sheet extends that into one column per size, and where the sizes share a marker the BOM carries a blended consumption rather than three separate ones.

The second path is through the trim. A grade that changes a strap length changes a webbing consumption; a grade that changes a panel area changes a foam sheet and a lining. Those are the lines that move on the BOM when a size is added, and a grading sheet that says which dimensions move is what lets the BOM be updated in one pass rather than in three.

What Is the Short Rule for Both Documents?

Write the pattern piece list as a table carrying a quantity, a material, a seam allowance per edge and a direction. Write the grading sheet with one column per size and a held note on every line that does not move.

Then ask for the cut file back, at a named unit and a named version. A programme that holds its own pattern can move a second run to any cut room that will take the file, and it never pays twice for the same development.

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