Generic shrinkage tools answer “wet to fired” for one dimension. A potter's real failure is a lid that no longer fits its pot — that needs two diameters, two shrinkage stages, and a clearance.
Total shrinkage is not drying % + firing %. The second stage shrinks an already-shrunk piece, so total = 1 − (1 − drying %) × (1 − firing %). With 5% drying then 7% firing that is 1 − 0.95 × 0.93 = 11.65%, not 12%. Fired diameter = wet diameter × (1 − total shrinkage).
Clearance here means fired lid diameter − fired pot rim diameter. A small positive clearance means the lid sits over the rim with a little room; a negative clearance means the fired lid is smaller than the rim and will not sit on top of it; a large positive clearance means a loose, wobbly lid. The verdict compares your fired clearance with the acceptable range you entered — the default 0.02–0.15 in is only a starting range, not a standard for every form, glaze or seating style.
The wet lid size you need is worked backwards: wet lid = (fired pot diameter + desired fired clearance) ÷ (1 − total shrinkage).
Do not trust a book figure for your clay body. Throw a test bar, mark a 10 in length while wet, measure it again bone dry, then again after firing. Drying % = (wet − dry) ÷ wet × 100, firing % = (dry − fired) ÷ dry × 100. Enter those two numbers above — that is the same two-stage arithmetic, measured on your own clay.
Estimates only. This page assumes pot and lid are the same clay body, dried and fired together, and that both shrink by the same percentages. It does not allow for glaze thickness, warping, or different drying conditions. Always test-fire a lid with its pot before committing to a run.