Tumbling Grit Schedule Calculator
Get a coarse-to-polish grit schedule sized to your rock’s Mohs hardness and your tumbler type, so you're not guessing how long each stage should run.
Grit schedule
Total: about 28 days across all four stages. Check progress every couple of days rather than tumbling on a fixed clock — stop a stage early once the rocks are smooth and the grit has broken down.
The standard four-stage method
The classic rotary-tumbling schedule runs roughly a week per stage for average-hardness material like agate or jasper (Mohs 6–7): a week of coarse grit to shape and round the rocks, a week of medium grit to erase the coarse scratches, a week of fine grit to erase those in turn and begin the shine, and a final week of polish to bring up the gloss. Softer material shortens every stage, since it wears down faster and over-tumbling can round it away to nothing before it's properly shaped.
Load size and shape matter too — a barrel that's too full or too empty tumbles unevenly, and mixing rocks of very different hardness in one batch means the softer ones finish (or disappear) well before the harder ones are ready.
Frequently Asked Questions
Why does rock tumbling need four separate grit stages?
Each stage removes the scratches left by the one before it. Coarse grit (60/90) grinds away rough surfaces and shapes the rocks; medium grit (150/220) removes the coarse scratches; fine grit (500) removes the medium scratches and starts a shine; and polish brings up the final gloss. Skipping a stage leaves the previous stage's scratches visible under the polish.
Why does hardness change how long a stage should run?
Softer material grinds away faster than hard material at the same grit, so a fixed one-week-per-stage schedule can round soft rocks down to pebbles before they're properly shaped. Scaling stage length to hardness keeps the rock in each grit only as long as it needs.
Why is a vibratory tumbler so much faster than a rotary one?
A rotary barrel only lets rocks tumble against each other as the barrel rotates, so contact is intermittent. A vibratory bowl keeps every rock in constant contact with the grit through continuous vibration, which does the same grinding and polishing work in a fraction of the time — typically a few days per stage instead of a week or more.
Should I follow the schedule exactly, or check on the rocks?
Treat the days as a starting plan, not a fixed clock. Check a rinsed sample partway through a stage: if the rocks are already smooth and rounded, move on to the next grit early; if they're still rough near the end of the planned time, give the stage a bit longer.
Educational hobby tool only. Actual timing varies with your specific tumbler, load size, and grit brand — check progress rather than tumbling on a fixed clock.