Tamper fit (58mm, 58.35mm, convex vs flat)

The diameter and base profile of a tamper relative to the basket. A 58 mm tamper in a 58 mm basket leaves a tiny gap; a 58.35 mm tamper fills the basket more completely. Bases are also flat (traditional) or convex (slightly domed).

Why it matters — A correctly fitted tamper produces an even compression across the puck. A loose-fitting tamper leaves a ridge around the basket walls that becomes a side-channel during brewing.

Good to know

• A 58.35 mm tamper fits most 58 mm baskets snugly — this is the spec specialty cafés prefer.
• Convex tampers were popular in the 2010s; modern consensus is that a flat tamper with good fit and WDT is simpler and equally effective.

Related: Tampers