Clay Weight Calculator
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Clay Weight Calculator
How much clay will you need? Estimate wet clay weight, fired capacity and shrinkage for your next cup, bowl, plate, vase, pot or tray. Then open a matching tool with your measurements filled in.
Plan your pottery with a little less guesswork
This free clay weight calculator from DIY Project Depot helps you plan the wet clay for a cup, bowl, plate, vase, rounded pot or rectangular tray. Compare wall and base thickness, allow for trimming, and see an estimate of the size and capacity after firing. Use it as a starting point, then check your clay and your making process.
Clay weight, shrinkage and capacity: frequently asked questions
How much clay do I need for a mug, bowl or plate?
Choose the closest form and enter its outer dimensions, wet wall thickness and wet base thickness. The calculator estimates the clay in the body, then adds your trimming allowance. It shows walls, base and extra clay separately. A handle, foot ring, lid or decoration needs additional clay.
Should I enter wet dimensions or the size after firing?
Either works: select Wet clay or After firing above the measurements. Top diameter, bottom diameter, width and height describe the outside of the body. Wall and base thickness always describe wet clay. The results show both wet and fired sizes so you can check your plan.
How does clay shrinkage affect the result?
Use total linear shrinkage from wet clay to your final firing. Wet size = fired size ÷ (1 − shrinkage ÷ 100). For a 100 mm fired dimension with 12% shrinkage, the wet dimension is about 113.6 mm. The starting 12% is an estimate; use a test bar and your own clay and firing schedule for a closer match.
What does wet clay density mean?
Density is the mass of a known volume of your workable clay, including its water. The initial 1.8 g/cm³ is only an editable starting estimate. For example, weigh a carefully measured 5 × 5 × 2 cm block of wet clay and divide its mass in grams by 50 to get g/cm³. Use the same clay consistency as your project and avoid trapped air. Dry or fired density is not a substitute.
Why can I set a separate base thickness?
A heavier base can change the amount of clay and the usable capacity significantly. Enter the wet thickness you plan for the base independently of the walls. Body height includes the base. The mass breakdown makes the effect of a thicker base visible.
What is the extra clay allowance for?
Extra for trimming adds a percentage to the calculated wall-and-base mass. Adjust it for your forming method, trimming and offcuts; the initial 15% is a planning allowance, not a requirement. Add clay for handles, feet and other parts separately. Wheel throwing or substantial reshaping may need more starting clay than this idealized body estimate.
How accurate is the capacity after firing?
It is an estimated internal volume filled to the brim, with your chosen wall and base thickness. Capacity scales with the cube of the remaining linear size: at 12% shrinkage, the volume factor is 0.88³. Everyday usable capacity will be lower. Glaze thickness, distortion and changes made while forming are not included. This is not an estimate of fired ceramic weight.
How are rounded pots and other forms calculated?
Pot uses a smooth rounded profile with an opening, a widest body diameter and a belly height. Other round forms use straight cylindrical or tapered walls and a flat base; Tray uses a straight rectangular body. Curved bowl profiles, a plate’s wide rim, organic outlines and surface relief are approximations. Choose dimensions close to your intended piece and check a real sample when precision matters.
Can I use inches instead of millimetres?
Yes. Changing units converts the existing measurements instead of changing the piece. In inch mode the starting clay weight is shown in pounds; capacity remains in millilitres. Shrinkage and the trimming allowance stay percentages.
Can I make a mold or slab template from these measurements?
Yes. The result includes links to Mold Studio and Slab Studio with the closest supported shape and dimensions already selected. Read the adjustments listed on each card before opening it. Some sizes or proportions must change to fit a tool’s limits. The Studios currently use the same wet thickness for walls and base, so a separately specified base thickness may change the resulting capacity and clay requirement. Review the design before buying.
Will a rounded pot open as exactly the same shape in a Studio?
Not always. Slab Studio approximates a rounded pot with two joined conical wall pieces and a base. Mold Studio opens the closest outward-opening bowl using the pot’s widest diameter; it does not create a narrow-neck, multipart or slip-casting mold. These differences are shown next to the links.
Do I need a pottery wheel or design experience?
No design experience is needed to use the calculator. Mold Studio and Slab Studio are designed for handbuilding with clay slabs, so you can explore those tools without a pottery wheel. The calculator itself is free to use and opening a Studio does not place an order.
Can I save a calculation or ask for help?
Use Copy this calculation link to keep the shape, dimensions, wall and base thickness, units and shrinkage. Wet density and trimming allowance are adjusted separately when the link is opened. If you are unsure which tool or size to choose, message us in the chat on this page or on Instagram @diyprojectdepot. A person will reply, not a robot.
Questions about your project? Use the chat on this page or message @diyprojectdepot on Instagram. We are happy to help.