Garment specs, which determine how well (or poorly) a piece of clothing fits, can make or break a design.

Incorrect garment specs lead to fit issues, multiple sample iterations, and if they get to the finish line – disappointed customers and high returns.

But you can skip the guesswork and create garment specs accurately and quickly using clothes you already have.

Now, this isn’t something I came up with – even pro technical designers have consistently utilized this method. It allows you to understand proportions, fit, and garment construction without starting from scratch.

Basing your garment measurement specs from existing clothes speeds up the design process by providing a baseline, which is especially useful for freelance fashion designers or technical designers working independently with fewer resources compared to those at big-name companies.

In this guide, I will teach you exactly how to spec a garment using clothes you already own, how to modify those measurements to your liking, and what to look out for when using this method.

Choosing the Right Reference Garment

To put it simply, you just need to select an existing garment that has the closest resemblance to the design you want to create. For example, if you’re designing high-waisted straight leg jeans, grab a pair of high-waisted straight leg jeans that fit well and have a similar style to your new design. Inspect the garment carefully, noting the fabric, fit, construction, and any other details that might affect the appearance of your new design.

Here’s a list of things to watch out for when selecting your reference garment:

1. Closest Fit: This is a no-brainer. Choose a garment that fits closely to your intended design. If your reference doesn’t match well, you’ll end up having to do more work figuring out how to adjust the measurements to get your desired fit.

2. Construction: Pay attention to how the reference garment is assembled. For example, if you want to create a piece with set-in sleeves, don’t use a dolman sleeve garment as your reference. You’ll end up having to figure out entirely different specs for the armhole, shoulder, and sleeve length which can lead to discrepancies.

3. Fabric and Material: The fabric’s weight / GSM (grams per square meter) and stretch significantly impact the fit. 

True Story: We once used the same garment specs to develop new t-shirt samples using a *slightly* different fabric. Since the new material was thicker and less stretchy, the t-shirt ended up tighter overall, and we struggled to get it over the head. The exact neckline measurement for a stretchy, low-GSM t-shirt did not translate well to a less stretchy, higher-GSM fabric.

What if I Can’t Find a Similar Garment?

Finding the perfect reference garment can be tricky, but I’ve learned some easy workarounds. 

Make sure to start with a good base – look for pieces that share similar construction elements, especially seam placements, as these form the foundation of your design. Once you have a good base, you can tweak it or incorporate other garment references to refine the design.

For example, when designing a square neckline tee, if you already have a reference garment with the ideal body fit but it has a crew neckline, search for another garment with the neckline shape you like.

Since you are using a mix of reference garments, be mindful of how measurements will be affected. For instance, the High Point of Shoulder (HPS) location varies depending on the neckline type; the HPS of a crew neck will be different from that of a square neckline.

Another tip is to create mock-ups using the base reference garment. You can draw over it, pin it, or add fabric / paper to simulate your design. In my previous example, you can get a fit model to try on the base garment and sketch out the neckline shape you desire. 

This also works for things like pockets and additional design details. You can sketch them on paper and experiment with their placement and size by attaching them to the garment using pins. These mock-ups are really helpful when visualizing the final outcome. 

Translating the Garment Measurements

At this point, you should already have your list of required POMs ready. With your garment in hand, carefully measure each part.

DISCLAIMER: This guide is not meant to teach you how to create POMs. If this is new to you, I suggest you refer to my POM Guide  and How to Measure Guide (with free templates). Note that creating accurate POMs is not something you can learn overnight, so for further study, I suggest studying old tech packs, or checking references such as the book The Spec Manual by Michele Wesen Bryan and Diane DeMers (which I have a review of on my YouTube channel ).

Remember, you don’t have to replicate every measurement. You might already have your “perfect” crotch specs or have a standard length in mind for your garment. If the reference garment’s measurements seem excessively long or short, feel free to subtract or add to get your desired garment fit.

What I like to do is use pins to mock-up the reference garment into the desired measurements. If I want to take in some width, I do this by pinning areas where I intend to remove fabric and have one of my fitters try on the mock-up. This way, I can visualize and fine-tune the fit before finalizing my garment specs.

Be mindful of how alterations in one measurement may impact other measurements. For example, any measurement adjustments on the shoulder width also impact the sleeve length because these parts are connected to each other. If you make the shoulder width wider, the sleeve hem will end up lower if left unadjusted.

Pro Tip: Sending your actual reference garment to the manufacturer, along with your tech pack, might seem like insider info, but it’s actually a pretty common practice in the fashion industry. Before developing new designs, we often hit up stores for “buying sessions.” We snag styles similar to what we want to develop pieces, give them a test run, then ship them off to our manufacturers along with the tech pack, complete with notes on any tweaks we want to make.

Grading from Existing Garments

Once you have finalized your measurements, the next step is to grade them across the planned size range. Grading is a topic of its own, but I have all the guides you need below!

1. Ultimate Guide to Grading Garments for Production
2. How to Create Graded Specs in a Garment Tech Pack
3. How to Auto Calculate Grade Rules in Your Tech Pack Using Formulas in Excel

Grading takes practice and experience, and it’s not something that can be mastered overnight. There is no magical equation or standard for grading each POM, and every unique design will require a new approach.

If you’re still unsure how to grade your garment or specific POMs, a practical method is to buy a whole size run of a similar garment and measure each size. If the budget is tight, you can buy size jumps – for example, XS, M, and XL, and then figure out the math for the sizes in between (S, L, etc.). 

I’ve done this before, and it’s a great way to not only tackle your current grading task, but also to learn how other fashion brands do their grading.

Creating the Garment Spec Sheet

Once all that’s done, you can now finalize your garment spec sheet and add it to your tech pack.

Here are a couple of guides to help you get through the next steps:

1. Step by Step Tech Pack Guide + Free Tech Pack Templates
2. What Goes in A Tech Pack?
3. What is a Garment Spec Sheet?
4. Guide to Technical Callouts in Apparel Tech Packs