Swing weight and MOI measure different things
Swing weight is a balance reading. The club sits on a scale with a fulcrum a fixed distance from the grip end, and the reading tells you how head-heavy it is. It is quick and every shop can do it, which is why most sets are built to one swing weight.
MOI (moment of inertia) describes how much the assembled club resists being rotated when it is swung from the grip end. It accounts for total weight and how that weight is distributed along the whole length. The idea behind matching on MOI is that each iron should take the same effort to swing, so tempo and feel carry from the 5-iron through the wedge.
The two do not agree. If every iron has the same MOI, the swing weight will not be the same, and the reverse is also true. You have to pick one.
The build
The set is a Mizuno Pro 245, 5-iron through pitching wedge, built in 2024 with 0.4-inch length steps. I worked out head weights and final assembly in a published MOI workbook (Jeff Waller’s “MOI Made Easy”), using my measured component weights and lengths. These are the as-built numbers from September 2024.
| Club | Length (in) | Head (g) | Loft (°) | Lie (°) | Swing weight | MOI (kg·cm²) |
|---|---|---|---|---|---|---|
| 5-iron | 37.7 | 254.6 | 23.0 | 62.0 | D1.5 | 2,746.9 |
| 6-iron | 37.3 | 260.8 | 26.2 | 62.5 | D1.8 | 2,749.4 |
| 7-iron | 36.9 | 269.8 | 29.0 | 62.75 | D2.0 | 2,749.4 |
| 8-iron | 36.5 | 275.4 | 33.0 | 62.75 | D2.2 | 2,751.1 |
| 9-iron | 36.1 | 282.8 | 37.25 | 62.75 | D2.5 | 2,751.3 |
| PW | 35.7 | 292.1 | 42.5 | 62.5 | D3.5 | 2,761.7 |
MOI values are calculated in the workbook from measured components, not read from an MOI machine.
What the numbers show
- The 5-iron through 9-iron sit within 4.4 units of each other, around 2,750.
- The pitching wedge finished about 15 units above the 5-iron.
- Swing weight climbs from D1.5 to D3.5. That is the expected side effect of matching MOI: as the clubs get shorter, they read progressively more head-heavy on a swing-weight scale.
- Head weight rises by about 6 to 9 grams per club, from 254.6 g in the 5-iron to 292.1 g in the wedge.
Compared with my earlier sets
I have built three iron sets toward an MOI target. The first was much less even.
| Club | 2023 set | Early 2024 set | Current set |
|---|---|---|---|
| 5-iron | 2,828.1 | 2,751.1 | 2,746.9 |
| 6-iron | 2,806.6 | 2,751.8 | 2,749.4 |
| 7-iron | 2,787.1 | 2,751.5 | 2,749.4 |
| 8-iron | 2,783.6 | 2,751.2 | 2,751.1 |
| 9-iron | 2,773.8 | 2,750.0 | 2,751.3 |
| PW | 2,768.2 | 2,758.0 | 2,761.7 |
| Spread, 5-iron to PW | 59.9 | 8.0 | 14.8 |
In 2023 the MOI fell steadily from the long irons to the wedge, about 60 units across the set. The two 2024 builds held it much tighter.
Swing weight matching works for most golfers. MOI matching is worth testing if your long irons and short irons feel noticeably different to swing. A fitting can check that on a launch monitor before anything is built.
All numbers on this page come from my own clubs, measured and recorded in my own build workbooks. Nothing here is drawn from client fittings. This is one golfer’s record, not a controlled study.