Hey everyone, I’m gonna keep this real—when I started working at the window latch company I’m part of, I kept getting asked the same question over and over: “Wait, 75mm? That’s 3 inches? Is that actually a standard size, or are y’all just making this up?” At first, I just rolled my eyes and went, “Yeah, it is,” but after a year of fielding this from homeowners, contractors, and even other suppliers, I realized most people don’t have a straight answer—so let’s break this down, no fancy jargon, just the real deal. 75mm (3 INCH)
First off, let’s get the basics out of the way: no, 75mm (3 inches) isn’t the only standard window latch size, but it’s way more standard than most folks think. I’ve been on calls where a homeowner buys a new vinyl window, pulls out the old latch, measures it, and goes “Wait, it’s 3 inches—all the hardware stores sold me 2.5-inch ones, what gives?” That’s because a lot of big box stores keep their stock super narrow, usually catering to newer construction homes that use smaller latch backsets, but that’s not the whole story.
Let’s talk about what a “standard” size even means here. For window latches, the number everyone cares about is the backset—That’s the distance from the edge of the window sash (the movable part that opens and closes) to the screw hole where the latch mounts. Backsets are what make or break a fit, right? If your backset’s 75mm, a 60mm one is gonna stick out too far or not reach, and vice versa. Now, the International Residential Code (IRC)—that’s the rulebook for most homes built in North America, which is where my main suppliers and clients are based—doesn’t mandate a single backset, but it does list common standard sizes. Let me check the notes our engineering team has on file, because I don’t wanna misquote this: they’ve got 60mm (2.375 inches), 70mm (2.75 inches), and 75mm (3 inches) as the three most widely accepted residential standards. Wait, why three? Because different window types, different manufacturers, different age of home.
Here’s the part that trips most people up: old windows. If your house was built before the 1990s, especially if it’s a wood window from a small local carpenter or a vintage home, 75mm was the go-to. I worked with a guy last month who was restoring a 1958 Cape Cod, and all his original latches were shot—every replacement he tried was too short, until he got our 75mm ones. Turns out, back in the day, most window manufacturers used 3-inch backsets because it was sturdier; longer backset means the latch screws into more of the sash frame, so less wiggle over time. That’s a big reason why when you’re replacing hardware on older homes, 75mm is way more likely to work than the 2.5-inch sizes the big boxes push.
Now, why do so many people think it’s not standard? Let’s be real—retailers only stock what sells, and the last 20 years have seen a boom in vinyl windows that use smaller backsets. New construction tends to use slimmer profiles, so they don’t need as long a backset. Big box stores see more demand for 60mm and 70mm, so they don’t order much 75mm. That’s why if you walk into Home Depot or Lowe’s right now, you might struggle to find a 3-inch latch—they’re there, just hidden in the back of a cabinet, not on the front shelf. That’s not because it’s not standard; that’s because retailers prioritized fast-selling sizes. I’ve had contractors call me in a panic because they showed up to a job site with the wrong latches, and we ship out next-day for a lot of our clients who run into that exact issue.
Let’s get into what makes a latch “standard” beyond just backset, because that’s not the only number. The height and width of the latch handle, the screw pattern, the distance between the two mounting holes—all that’s standardized too, and 75mm (3-inch) ones match that. Our team tests every batch to make sure the screw holes line up with IRC specs, so when a customer says “my old latch is 3 inches,” they can order ours and not have to drill new holes. I can’t tell you how many emails we get that just say “my latch is 3 inches, send the right ones” because they don’t wanna mess up their window.
Wait, but what about commercial windows? A lot of folks only care about residential, but I should mention this too. Commercial window standards (from the National Fenestration Rating Council, NFRC) have a couple more sizes, but 75mm is still a common standard for small to mid-sized commercial spaces, like office break rooms or storefronts that aren’t massive. The bigger commercial jobs use larger backsets, but 3-inch is still in the mix, especially for retrofits of older commercial buildings that used those same sizes back in the day.
I’ve also heard people say “metric is weird, 3 inches isn’t exact,” but let’s be clear: 75mm is a metric conversion of 3 inches, and it’s been standardized both ways for decades. A lot of manufacturers switched between metric and imperial in the 90s, so you’ll see labels that say both, because that’s what most of the market uses. Our latches are labeled with 75mm first, because that’s the industry standard term in our supply chain, but we always note it’s 3 inches for anyone who works in imperial. That’s not a mistake—that’s how standard sizes work, they overlap for different markets.
Now, let’s talk about why this matters, beyond just fitting a latch. If you get the wrong size, your window is unsafe. A latch that’s too short won’t lock tight, which is a security risk, and it can make the window rattle when it’s windy. I had a customer last year who bought a cheap 2.5-inch latch for his 1960s window, and it fell off mid-winter, leaving his window stuck open. That’s a nightmare. 75mm latches are built to handle that extra length, so they’re more durable for older, heavier wood windows too—something the smaller, newer latches can’t handle as well.
I wanna be transparent, though: is 75mm the only standard? No. If you have a brand-new vinyl window from a big national manufacturer, odds are it’s 60mm. If you have a mid-range window from the 2000s, it’s 70mm. But 75mm is definitely a standard, it’s just a underrated one that’s super common for retrofits, vintage homes, and any window that needs a sturdier mount. Our company has been supplying these for 8 years now, and we sell more 75mm than any other size—turns out, a lot of contractors and homeowners know it’s standard, they just can’t find it at regular stores.
That’s the thing about standards, right? They’re not universal, but they’re widely accepted for specific use cases. No one argues that a #2 Phillips screwdriver is standard, even though there are other sizes. Same with 75mm window latches—they’re a standard for residential retrofits, older construction, and any application where a longer, sturdier backset is better. The confusion just comes from where you shop, not the actual industry specs.
If you’re someone who’s struggled to find the right latch, whether you’re replacing one on a old window or a contractor working on a job that needs consistent sizes, hit us up. We supply bulk to contractors and small quantities to homeowners, all of our 75mm latches are tested to meet those standard specs, so you don’t have to worry about them not fitting. No more running around hardware stores chasing the wrong size, no more drilling new holes when you don’t have to. Just reach out, we can hook you up.
50mm (2 INCH) References: International Residential Code (IRC) Section R310.1.2 Door and Window Hardware; National Fenestration Rating Council (NFRC) Standard 103-19; Historic Window Restoration Association Hardware Specification Guidelines.
Chang Chuan Enterprise Co., Ltd.
Chang Chuan Enterprise Co., Ltd. is known as one of the most professional 75mm (3 inch) manufacturers and suppliers in Taiwan, China. We warmly welcome you to buy high quality 75mm (3 inch) at competitive price from our factory. For customized service, contact us now.
Address: No.93, Chang-an Lane, Antung Village, Hsiu Shui Hsiang, Changhua Hsien, Taiwan
E-mail: cce@ccecasters.com
WebSite: https://www.ccecastors.com/
