How much bigger should a bowl blank be than the finished bowl?

Allow at least 10mm extra on the diameter (5mm each side) for truing up the blank on the lathe. For depth, add 10-15mm for the mounting tenon or waste block. For green (wet) wood, add an extra 10% to allow for shrinkage as the bowl dries.

What is a good wall thickness for a turned bowl?

For dry-turned bowls, 6-10mm is typical for decorative pieces, 8-12mm for functional bowls. For green-turned bowls that will distort as they dry, turn to 10% of the diameter (e.g., 25mm walls for a 250mm bowl) and re-turn after drying.

What speed should I turn a bowl blank at?

Use the safe-speed band: the blank diameter in inches multiplied by RPM should stay between roughly 6,000 (low) and 9,000 (absolute maximum). A 200mm finished bowl gives a 220mm (~8.7 inch) blank, so the upper guide is about 900 RPM (8,000 ÷ 8.7) and the calculator shows this as the "suggested upper speed". For roughing an unbalanced blank, START nearer 600-700 RPM (6,000 ÷ 8.7) and raise the speed only as the blank trues up and runs smoothly.

What size faceplate should I use?

The faceplate diameter should be roughly one-third of the bowl diameter. For a 200mm bowl, use a 60-75mm faceplate. The faceplate must be fully supported by solid wood - never let screws go into the part of the blank that will become the bowl interior.

WoodCalcs

Bowl Blank Calculator — Blank Dimensions for Turned Bowls

Calculate bowl blank dimensions and wood required for turned bowls.

Wood Species

Finished Bowl Diameter

Outside diameter of the finished bowl (mm)

Finished Bowl Depth

Inside depth/height of the finished bowl (mm)

Wall Thickness

Target finished wall thickness; for green twice-turning use ~10% of bowl diameter

How We Calculate This

This calculator determines the minimum blank dimensions needed to turn a bowl to your specified finished size.

Blank sizing

Blank diameter = Finished diameter + 20mm (10mm each side for truing)

Blank thickness = Finished depth + 15mm (for tenon and mounting waste)

Safe speed

The diameter (in inches) × RPM should stay within roughly 6,000-9,000 (Doc Green / Turn A Wood Bowl).

Suggested upper speed = 8,000 / Diameter in inches. Begin roughing an unbalanced blank lower, nearer 6,000 / Diameter in inches, and raise the speed only as the blank trues up.

Wall thickness

For green (wet) twice-turning, rough the walls to about 10% of the bowl diameter(e.g. ~20mm for a 200mm bowl) so the bowl can move freely as it dries, then re-turn once dry. The calculator flags whether your entered wall meets this target.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.