Baltic Birch Thickness Chart: 3–30 mm
Actual thickness in millimetres and inches, the US performance category each one matches, ply counts, sheet weight and how many sheets are in a pack.
18 mm is not 3/4 inch — and neither is American 3/4 plywood
18 mm measures 0.709", which is 0.041" short of a true 3/4". That is the figure usually quoted at people switching to Baltic birch, and on its own it misleads — a US panel sold as 3/4 inch is not 0.750" either.
American plywood is graded by Performance Category. Under PS 1-22, Table 10, a sanded 3/4 panel measures 18.65–19.45 mm and a 23/32 panel 17.86–18.65 mm. An 18 mm sheet falls inside the second band.
18 mm ≈ 23/32", not 3/4" — and since much of the American plywood sold as “3/4 inch” ships as a 23/32 panel, the two line up in practice. The pattern holds down the range: 12 mm lands in 15/32 rather than 1/2, 15 mm in 19/32 rather than 5/8. Every metric thickness sits one American category below the fraction it is named by.
| Metric | Decimal inch | Called | US category, PS 1 | lb / sheet 5x5 · 4x8 | Plies | Sheets / pack |
|---|---|---|---|---|---|---|
| 3 mm | 0.118" | 1/8"−0.007" from it | outside | 10.5 · 13.4 | 3 | 130 |
| 4 mm | 0.157" | 5/32"+0.001" from it | outside | 13.9 · 17.9 | 3 | 100 |
| 5 mm | 0.197" | 3/16"+0.009" from it | outside | 17.4 · 22.3 | 5 | 80 |
| 6 mm | 0.236" | 1/4"−0.014" from it | 1/4 | 20.9 · 26.8 | 5 | 65 |
| 8 mm | 0.315" | 5/16"+0.002" from it | 5/16 | 27.9 · 35.7 | 7 | 50 |
| 9 mm | 0.354" | 3/8"−0.021" from it | 11/32 | 31.4 · 40.2 | 7 | 44 |
| 12 mm | 0.472" | 1/2"−0.028" from it | 15/32 | 41.8 · 53.6 | 9 | 33 |
| 15 mm | 0.591" | 5/8"−0.034" from it | 19/32 | 52.3 · 66.9 | 11 | 26 |
| 18 mm | 0.709" | 3/4"−0.041" from it | 23/32 | 62.8 · 80.3 | 13 | 22 |
| 21 mm | 0.827" | 13/16"+0.014" from it | 13/16 | 73.2 · 93.7 | 15 | 19 |
| 24 mm | 0.945" | 15/16"+0.007" from it | outside | 83.7 · 107.1 | 17 | 17 |
| 27 mm | 1.063" | 1-1/16"+0.000" from it | outside | 94.1 · 120.5 | 19 | 15 |
| 30 mm | 1.181" | 1-3/16"−0.007" from it | outside | 104.6 · 133.9 | 21 | 13 |
Called is the fraction the trade names the panel by, with how far it actually sits from it. US category is the PS 1-22 band it falls inside (Table 10, sanded grades); outside means it falls between two bands. Note that PS 1 covers structural plywood — hardwood plywood under ANSI/HPVA HP-1 has no thickness table at all, clause 2.2.5 leaving it to the manufacturer. Weight is calculated at 680 kg/m³, our working figure for birch — a whole load or a price in any unit follows from it in the converter. Ply counts are typical and always odd; sheets per pack are our own figures, reconciled against warehouse volume.
Why the pack count falls as thickness rises
A pack is built to a fixed height, not a fixed sheet count. So 130 sheets of 3 mm and 22 sheets of 18 mm occupy about the same space and weigh roughly the same.
The practical consequence is convenient: a pack is a constant unit of volume whatever you order. If a truck takes a given number of packs of 12 mm, it takes the same number of packs of 18 mm. That is why we sell and quote by the pack rather than by the sheet — it makes a mixed load planned in packs come out right the first time.
Our minimum is five packs, and they can be five different thicknesses and grades.
What each one is usually bought for
- 3 – 6 mm
- Laser and CNC work, model making, drawer bottoms, back panels, bending and lamination.
- 9 – 12 mm
- Drawer sides, small case work, jig stock, speaker baffles, toy and display parts.
- 15 – 18 mm
- Cabinet carcases, shelving, worktops, furniture structure. The volume thicknesses.
- 21 – 30 mm
- Stair treads, heavy shelving, machine tables, structural furniture components.
Which of these we hold on the floor changes by format and warehouse — see 5x5 and 4x8.
Not sure which thickness
Describe the part rather than the panel — what it is, how it is loaded, how it is joined — and we will tell you what shops building the same thing actually use. It is a faster conversation than a spec sheet.