Pottery Throwing Speed by Form Calculator
Find the optimal wheel speed (RPM) for throwing different pottery forms based on diameter and clay type.
Wheel speed is critical in pottery throwing. Too fast and the clay flies off center or collapses. Too slow and you cannot pull walls effectively. The optimal RPM depends on the diameter of the piece, the stage of throwing, and the clay body.
Speed-Diameter Relationship
As diameter increases, the outer rim moves faster at any given RPM. The rim speed (surface velocity) should stay roughly constant for comfortable throwing:
Rim speed = RPM × π × Diameter
A comfortable rim speed is approximately 90–150 cm/s for most throwing operations.
Solving for RPM: RPM = Target rim speed / (π × Diameter)
Recommended RPM by Form and Stage
| Form | Diameter | Centering RPM | Opening RPM | Pulling RPM | Finishing RPM |
|---|---|---|---|---|---|
| Espresso cup | 6–8 cm | 200–300 | 150–200 | 100–150 | 40–60 |
| Mug | 8–10 cm | 180–250 | 120–180 | 80–120 | 30–50 |
| Bowl (small) | 12–15 cm | 150–220 | 100–150 | 70–100 | 25–40 |
| Bowl (large) | 20–30 cm | 100–150 | 60–100 | 40–70 | 20–30 |
| Dinner plate | 25–30 cm | 100–140 | 50–80 | 30–50 | 15–25 |
| Vase / cylinder | 10–15 cm | 150–220 | 100–150 | 60–100 | 25–40 |
| Large platter | 35–45 cm | 60–100 | 40–60 | 25–40 | 10–20 |
Centering vs. Pulling
Centering requires the highest speed — the centrifugal force helps align the clay. As you open and pull walls, reduce speed progressively. Thin walls at high speed will collapse from centrifugal force.
General rule: reduce speed by roughly 30–40% from centering to pulling, and another 50% for finishing/trimming.
Clay Body Adjustments
| Clay Type | Speed Adjustment |
|---|---|
| Porcelain | Reduce 10–20% (soft, collapses easily) |
| Stoneware | Standard speed |
| Earthenware | Standard speed |
| Raku | Standard to +10% (grogged, more stable) |
| Heavily grogged | +10–15% (resists centrifugal force) |
Porcelain is notorious for collapsing at speed. Reduce RPM by 10–20% compared to stoneware for the same form.
Worked Example — 12 cm Stoneware Mug
Centering: 200 RPM (rim speed = 200 × π × 0.12 = 75 cm/s — comfortable). Opening: 150 RPM. Pulling walls: 100 RPM. Finishing/collaring: 40 RPM.
For the same mug in porcelain: reduce each stage by 15%. Centering: 170 RPM. Opening: 130 RPM. Pulling: 85 RPM. Finishing: 35 RPM.
Trimming Speed
Trimming (turning the leather-hard pot upside down to refine the foot) uses moderate speed: typically 100–180 RPM for small forms and 60–100 RPM for large forms. The piece is held by friction or a chuck, so excessive speed risks the piece flying off.
Variable Speed Wheels
Modern electric wheels allow continuous 0–300 RPM adjustment. If you are using a kick wheel, your effective range is roughly 30–120 RPM, so plan forms that work within that range.