Size Grading and Spec Sheets. Fit One Size. Get Every Size Right.
Size grading and spec sheets decide whether every size of a style fits as intended. Here is how grading works, what goes on a spec sheet, and the mistakes behind fit problems in bulk.
Size grading is the process of taking a product developed in one base size and scaling its measurements up and down to create every other size in the range. A spec sheet (measurement specification sheet) records those measurements for each size, with the points of measure, how to measure them and the tolerance allowed. Together they make sure a size S and a size XL of the same style fit the way the brand intends.
Many fit problems start on the spec sheet, with a measurement defined loosely, a grade rule applied wrongly or a tolerance never written down, so they show up later as returns and rejected production.
Key takeaways
- A style is developed and fitted in one base size first. The other sizes are graded from it.
- Grade rules set how much each measurement changes from one size to the next.
- A spec sheet lists the points of measure, how to measure them, the measurements for every size and the tolerance for each.
- Tolerances tell the factory and quality team which measurements are acceptable.
- Grading errors often appear only in bulk, so check graded sizes with a size set sample.
Fit the base size first. Then grade.
The base size (or sample size) is the size a style is designed, sampled and fitted in. It is usually in the middle of the range, such as M for tops or a mid shoe size for footwear. The brand fits it on a fit model, a person whose body matches the brand's size standard.
Grade rules. One for every measurement.
Grading uses grade rules: the amount each measurement grows or shrinks between neighbouring sizes. For example, a brand might grade chest width up by a set amount per size, and body length by a smaller amount. Think of it as a recipe that turns one approved size into a full range.
A few principles apply in most categories:
- Not everything grades equally. Width measurements usually change more than lengths, and some details, such as pocket size or button spacing, may not change at all.
- Steps can change across the range. Many brands use larger steps for bigger sizes. The point where the step changes is called a break point.
- Different fits may need their own base size. Plus, petite and tall ranges often have their own base size and grade rules rather than being stretched from the regular range.
- The pattern and the spec must agree. Grading is done on the pattern, often in pattern-making software, and the results are written into the spec sheet. If the two disagree, the factory will follow one and the quality team will check against the other.
Footwear has its own version of grading, where lasts, soles and components are scaled across shoe sizes.
Seven parts. Every size on one page.
A complete spec sheet includes:
- Style information. Style name and number, season, base size, size range and version date.
- Points of measure. Each measurement, with a code and a clear name, such as "chest width, 2 cm below armhole".
- How to measure. A short description or diagram showing exactly where the measurement starts and ends.
- Base size measurements. The approved measurement for each point in the base size.
- Graded measurements. The measurement for every size in the range.
- Tolerances. The plus or minus allowed for each point.
- Sample measurement columns. The actual measurements of each sample, the difference from spec, and comments.
Six fit problems teams tell us about. And the cause behind each.
The base size was graded before the fit was approved, so every size inherited the fault.
Grade the other sizes only once the base size fits.
Points of measure (POMs) were unclear. "Chest" could mean the full circumference or the width measured flat, which is half. "Length" could start at the shoulder seam or the highest point of the shoulder.
Write each definition once, add a diagram, and reuse the same POM library across styles so factories learn it.
There were no "how to measure" notes, so each measured in its own way.
Add a short note or diagram for every point of measure.
Tolerances were missing, so every millimetre became an argument.
Give every point a tolerance, with tighter ones on critical fit points such as chest, waist and hip.
The pattern was regraded but the spec sheet was not.
Update the spec sheet every time the pattern changes, and version both.
Fit comments sat in emails and photos outside the spec, so the next sample repeated the same problem.
Record every fit comment on the spec sheet, next to the measurement it concerns.
Follow one dress from base size to size set
Imagine Amira, a technical designer at a womenswear brand, working on a new wrap dress:
- She agrees the base size, M, and the fit model before the first sample.
- After each fit session, measurements and comments go next to the spec.
- Only once the fit is approved is the full range graded.
- A size set confirms the grading, and she locks and versions the sheet.
Agree the base size. Lock the spec.
- Choose the base size and fit model. Agree them before the first sample.
- Pick the points of measure. Start from a standard list for the category and remove the ones that do not apply.
- Write base size measurements. Send them with the tech pack for the proto sample. See our guide to what a tech pack is.
- Measure and fit each sample. Record actual measurements next to the spec and note fit comments.
- Adjust and refit. Update the base measurements after each fit session until the fit is approved.
- Apply grade rules. Grade the approved base size across the full range.
- Set tolerances. Add a tolerance for every point of measure.
- Check with a size set. Ask the factory for samples in several sizes to confirm the grading. Our guide to the types of samples in fashion explains size sets and fit samples.
- Lock and version it. Every change after approval gets a new version and a note.
Part of the tech pack. Not a side file.
The spec sheet is part of the tech pack, alongside sketches, the bill of materials, construction details and labelling. For a few styles with one factory, a careful spreadsheet can work. As the range grows, keeping a separate spec in step with the tech pack and every fit comment gets harder.
A PLM (product lifecycle management) system keeps specs, fit comments and approvals on the product record, with every version saved. If you are new to PLM, read our guide to what PLM is.
How Polluxa helps
Polluxa PLM is product lifecycle management software for fashion, footwear, beauty, consumer goods and manufacturing brands. Our PLM software for consumer brands keeps specs, samples and fit approvals together on one product record.
- Nobody works from an old spec. With Product Development, every product has one record with its full version history, so everyone sees the latest spec.
- Fit approvals no longer get lost. Samples and fit approvals are tracked for each style.
- Fit comments no longer need long emails. Use visual markups to align teams on design and quality expectations.
- Specs no longer travel in a separate file. The Tech Pack Generator lets you add images, annotations, markups, specifications and comments, then download a supplier-ready file. Templates can be customised by product category.
- Suppliers no longer see more than they need. Each supplier sees only the products you share with them.
Start this week
- Write a one-line definition and a diagram for your ten most used points of measure.
- Add a tolerance to every point on your next spec sheet.
- Ask for a size set on your next new style before you approve bulk.
When you want to see this on your own styles, book a demo.
Frequently asked questions
Size grading is scaling an approved base size pattern and its measurements up and down to create every size in the range. It follows grade rules that set how much each measurement changes between sizes.
A grade rule is the amount a single point of measure changes from one size to the next. Each point, such as chest width or sleeve length, has its own rule, and the rules can change at a break point in the range.
A spec sheet holds the measurements, points of measure and tolerances. A tech pack is the full instruction set for the factory, and the spec sheet is one part of it.
Tolerance is how far an actual measurement may differ from the spec and still pass. It is written as a plus or minus value for each point of measure.
Usually a pattern maker or technical designer, either at the brand or at the factory. The brand should always review the graded spec sheet and check it with a size set sample.
