If you're currently starting every new jean by sending some blurry screenshots to your factory and hoping they can reverse-engineer the fit from a Pinterest board, please stop.
You're bleeding money, time and quite possibly customer trust.
In the garment world, we have something called a block. And if you're trying to build a denim brand where customers can come back season after season with some idea of how your jeans are going to fit, blocks are pretty bloody useful.
So what actually is a block?
A block is a basic foundation pattern that's been developed and fitted to your brand's body measurements and fit requirements.
Think of it as the technical starting point underneath the design. Before we've added the exciting wash, giant turn-ups, horseshoe leg, weird pockets, studs or whatever else you've decided absolutely needs to be on this pair of jeans, we need to know the foundation underneath it all actually works.
The block sets things like the waist-to-hip relationship, the rise, the seat shape, the balance and the proportions that we know work for the customer we're designing for.
That's why choosing your base size matters. The two go hand in hand. Your base size establishes who you're fitting. Your block establishes how you're fitting them.
It's a bit like the chassis of a car. You can change the paint, the leather seats and the headlights, but you're starting from a structure you already know works. Although, unlike an actual car chassis, we're allowed to chop ours up quite a lot without anyone dying.
1. Consistency of fit
We've all been there.
You buy a pair of jeans from a brand in a size 12 and they're perfect. The heavens open. Angels sing. You have finally found THE JEANS.
A month later you confidently order another pair from the same brand in a size 12, and you can't get them over your thighs.
Obviously, different styles are supposed to fit differently. A low-rise baggy jean shouldn't fit like a high-rise slim straight. But there should still be some underlying logic to the way a brand fits.
That's where blocks come in. Instead of every new style being developed from whatever pattern the factory thinks looks roughly right, you've got a known starting point. You already understand how your customer is shaped and how you've chosen to fit the waist, hip, rise and seat. Then you deliberately change those things to create the new silhouette.
The important word there is deliberately.
2. You probably don't need one magical jeans block
This is where it gets slightly more complicated.
You don't necessarily develop one single jeans block and use it for absolutely everything until the end of time. Your super-stretch skinny and your rigid 100% cotton baggy are asking very different things of the fabric and the body. Forcing both out of exactly the same block would rather defeat the point.
As your denim range grows, you might end up with a small family of trusted blocks. Perhaps a rigid denim block, a stretch block and a relaxed or baggy block. If different rises become important enough to your range, you might establish those too.
There's no magic number of blocks every denim brand needs. The point is to build the ones that are useful for your product range, rather than starting every new jean from nothing.
3. Consistency of grading
A good block isn't just one beautifully fitted sample size. It should have a grading strategy behind it too.
Once you've worked out how a block needs to grow and shrink across your size range, you've got a much stronger starting point for the next style developed from it.
That doesn't mean you blindly slap exactly the same grade onto every future pair of jeans regardless of the design. Different silhouettes may need adjusting. But you're no longer asking the factory to invent your sizing logic from scratch every time.
So when you turn your straight jean into a wide leg, you're changing the bits that need to change because of the design, rather than accidentally changing the whole fit because Barry at the factory found a different grade chart.
If you want to go further down that particular rabbit hole, I've written a whole article about grading. Of course I have.
4. It gives you a consistent starting point
Starting from a blank piece of paper is for artists. We are clothing engineers.
When you start from a block, a huge chunk of the fundamental fit work has already been done. You're not asking:
Where should the front rise sit?
How much shape do we need through the seat?
Why is the waistband gaping?
Why is there a weird amount of fabric under the bum?
Where should the hip sit?
You've already spent time answering those questions. Now you can concentrate on turning that foundation into the jean you're actually trying to make. Maybe we're widening the leg, changing the rise, adding a barrel shape, playing with the yoke, changing the pocket shape or making the whole thing deliberately oversized.
Fine. We're making those changes from something we understand.
5. It can save an obscene amount of time
Developing jeans from scratch can take round after round of sampling, and sampling is soooo expensive. Every time a sample goes backwards and forwards, you're paying for another sample, another courier, another fit session and another chunk of your critical path.
If you start from a tried-and-tested block, you're not expecting the first sample to be magically perfect. But you should be starting a lot closer.
So instead of using sample 1 to discover that your entire rise and seat shape don't work for your customer, you can use it to check whether the new design is doing what you intended.
That's a much better use of a sample.
6. It stops every factory having a different version of your customer
This is a big one.
Let's say Factory A develops your first pair of jeans. They use their block. You tweak it over five rounds of sampling until you finally get something you love.
Great.
Then you want to move a style to Factory B. Factory B has its own block, its own standard measurements and its own grade rules. Suddenly you're back at sample 1, asking why the bum looks weird again.
If you've established your own blocks, specs and grade rules, the technical fit belongs to your brand rather than living entirely inside one supplier's pattern room. That gives you much more control when you change factories, add suppliers or start producing somewhere new.
It doesn't mean you can chuck a pattern at any random factory and get an identical product. Fabric, machinery, construction, wash and production capability all still matter. But you're giving everyone the same technical starting point, and that makes a massive difference.
"Do I need a block for every single jean?"
No. Please don't go and commission 17 blocks because you've read this.
Look at what you're actually selling. If your whole brand is built around rigid denim, one really strong rigid block might be where you start. If you sell rigid and stretch, you may need different foundations. If one silhouette makes up 70% of your business, that's probably more useful to establish than a low-rise flare you sell twice a year.
Build your block library around your real range. You can add to it as the brand grows.
Your hero style might already be your block
You might already have the answer sitting in your warehouse.
Maybe there's one jean your customers are obsessed with. The reviews are brilliant, returns are low, customers own it in four washes, and every time you launch it in a new colour it sells.
That jean is telling you something.
Rather than reinventing the fit every time you develop something similar, we can look at what makes it work and use that to establish a trusted foundation for future styles.
That doesn't mean photocopying the pattern and changing the pockets forever. It means understanding what's working (the waist-to-hip relationship, the rise, the seat, the thigh, the balance, the grade) and keeping that DNA while you develop something new.
Blocks aren't "set and forget"
A word of caution: having a block doesn't mean you can develop every future jean without fitting it.
I wish.
Change the denim and the fit can change.
Go from stretch to rigid and it definitely will.
Change the wash and you might affect shrinkage, stretch, recovery and handfeel.
Change the rise and you've changed how the garment sits on the body.
Change the leg shape and you need to check the balance again.
Even two washes of what's supposedly the same jean can behave differently. So yes, we still fit samples.
The block isn't there to remove product development. It's there to give product development a known starting point, so you're making a surgical tweak rather than engineering a whole new fit from scratch.
Your block is only as good as the body you built it around
This is why all of this goes hand in hand with choosing your base size and fit model.
You can create the most technically beautiful block in the world, but if you've built it around the wrong body, congratulations. You now have an extremely consistent way of making jeans that don't fit your customer.
Your base size, fit model, body measurements, block and grading all need to work together. They're not separate technical exercises. They're your fit system. Once you start thinking of them like that, developing a range gets a lot less random.
Consistency is quietly doing a lot of your marketing for you
Nobody is going to post an Instagram Story saying "OMG the waist-to-hip relationship across this brand's core block architecture is SO consistent 😍".
At least I hope not.
But they will say "I always buy my jeans from them because I know they'll fit."
A customer doesn't need to know you have blocks. They don't need to know what grading is, or that you spent three hours discussing the shape of a back rise. They just know they bought jeans from you, loved the fit, bought another pair and loved those too.
That's one of the quietest and most effective bits of marketing you'll ever do.
Ready to stop starting from scratch?
If every new jean feels like developing an entirely new brand, if your factory keeps changing the fit, or if you've got one brilliant bestseller but no idea how to turn it into a reliable foundation for the rest of your range, it might be time to look at your blocks.
I can help you work out what you actually need, rather than building a giant library of patterns you'll never use. The goal isn't to have loads of blocks. It's to have a technical foundation you can trust.