Golf Driver Shaft Flex Chart: Find the Right Flex for Your Swing Speed

Match your driver shaft flex to your swing speed roughly Senior for 70–89 mph, Regular for 90–99 mph, Stiff for 100–109 mph, and X-Stiff for 110+ mph on a Steadfast Jupiter One shaft. That's a solid starting point, not a universal rule, because shaft flex isn't standardized across brands a "Stiff" in one shaft can load and release closer to a "Regular" in another. The full chart is below, along with why the ranges shift by brand and how to confirm you're actually in the right one before you buy.

Quick question before you scroll to the chart

What flex are you playing right now and be honest, did you pick it because a launch monitor told you to, or because your buddy plays it, or because "regular" just sounded like the safe, average choice?

You're not alone if it's the second or third one. Flex is one of the most guessed-at numbers in golf, and it's also one of the easiest to get wrong quietly for years without noticing, because a mismatched flex doesn't always feel bad. It just quietly costs you consistency.

Driver Shaft Flex Chart (Swing Speed → Flex)

This chart is built from the actual flex specs on our Jupiter One Driver Shaft, so it reflects real, purchasable ranges rather than a generic industry average:

(Weight and torque get lighter and lower as flex increases, which is why "just go up a flex" isn't always the fix — see below.)

A few things worth knowing before you treat this as gospel:

If you're right on a line, tempo breaks the tie. A smooth, unhurried 92 mph swing can load a shaft differently than an aggressive, fast-transition 92 mph swing. If your number falls within 3–4 mph of a boundary, the way you swing matters as much as the number itself.

Chasing "stiff" because it sounds better is one of the most common mistakes we see. A shaft that's too stiff for your speed won't load properly, which usually shows up as thin contact, a weak low fade, or just less distance than a properly matched flex would give you not a "more powerful" ball flight.

This exact chart is specific to Jupiter One. Because flex isn't standardized industry-wide, a shaft labeled "Stiff" from another brand can play noticeably softer or firmer than ours at the same swing speed. If you're comparing across brands, compare torque and weight, not just the flex letter.

Why doesn't every brand use the same numbers?

Here's the part that trips people up: "Regular" isn't a fixed physical spec the way "45.5 inches" is. It's a category each shaft maker assigns based on how that particular shaft's profile  its bend point, wall thickness, and taper behaves under load. Two shafts can both say "Stiff" on the label and perform noticeably differently in your hands, because the label describes a feel and behavior range, not a single measurable number every brand agrees on.

That's exactly why we publish the torque and weight next to the flex name in the chart above, instead of just the letter. If you already know roughly what torque and weight has worked for you in the past, you can use that to sanity-check the flex label on anything you're considering ours or anyone else's.

Are you actually in the wrong flex right now?

Ask yourself honestly:

• Do your mis-hits feel inconsistent — sometimes a push, sometimes a pull, sometimes just short — rather than one repeatable miss?

• Have you gone up a flex at some point "to be safe" without ever hitting balls side-by-side with the lower flex?

• Is your current shaft whatever came stock with the driver, rather than something chosen for your actual swing speed?

If two or more of those sound familiar, there's a good chance your current flex is a guess wearing a label, not an actual fit.

Driver flex vs. everything else in your bag

One more thing worth knowing: your driver flex doesn't automatically carry over to the rest of your bag. Driver shafts are longer and lighter, so they load and release differently than the shorter, heavier shafts in your irons, or the in-between profile of a fairway wood shaft. It's common and completely normal to play a different flex in your driver than in your 3-wood. If you're shopping a matching fairway shaft, don't assume the same letter automatically applies; check the swing-speed range for that specific shaft.

Get a real number, not just a guess

A chart gets you close. It doesn't replace actually testing the shaft with your swing.

• Take the Steadfast Shaft Selector Quiz — a faster, more personal way to land on a flex than eyeballing a table.

• Shop the Jupiter One Driver Shaft — see all four flex options, specs, and pricing.

• Read: Golf Shaft Flex Explained — Regular vs Stiff vs Senior — for the deeper "why" behind each flex category.

• Read: Senior Driver Shaft Review — How Wayne Fixed His Slice — a real example of what happens when the flex actually matches the swing.

• Shop the Jupiter One Driver + 3 + 5 Wood Bundle — once your driver's dialed in, your fairway woods are the next place mismatched flex tends to hide.

The bottom line

The chart gets you 90% of the way there. Your tempo, your mis-hit pattern, and a few honest minutes on a launch monitor (or our quiz) get you the rest of the way. Don't get shafted by a label that doesn't match how you actually swing.