Free Ceramics and Pottery Studio Calculators for American Potters

Clay shrinkage is the percentage reduction in size that happens in two stages: first when the clay dries by losing water, and again when it is fired in the kiln during vitrification. For a US potter, it matters because if you are making a mug that needs to fit a standard-size coaster or a dinner plate that has to fit a specific kiln shelf, your wet size and your fired size are not the same thing. A mid-fire stoneware piece typically shrinks 10 to 12 percent total. If you throw a bowl 12 inches wide and your clay shrinks 11 percent, the finished bowl will be about 10.68 inches across. For a production potter filling an order for a restaurant in Nashville who specified exact dimensions, that gap is the difference between a successful delivery and a returned shipment.

Most online shrinkage calculators accept a single percentage and apply it in one step from wet to fired. Our tool tracks shrinkage across all three stages of the ceramics process: wet clay to bone-dry greenware (drying shrinkage), bone-dry greenware to bisque fire (first fire shrinkage), and bisque to glaze fire (second fire shrinkage). This lets you know exactly what size you are working with at every stage of production, which matters when you are trimming lids, adding handles or feet, or assembling multi-piece forms that need to fit each other through all stages of firing without distortion or mismatch.

In ceramics, “parts” is a relative unit. A recipe might call for 40 parts silica, 20 parts feldspar, and 15 parts whiting. These are not grams or ounces; they are ratios. To convert to a usable batch, you divide each ingredient by the total number of parts and multiply by your target batch weight in grams. Percentage recipes have already done that first step: every ingredient is expressed as its share of 100 percent. Our Glaze Batch Scaler handles both formats. You choose whether your recipe is in parts or percentages, enter the numbers, set your batch size in grams, and the tool outputs the weight to measure for each ingredient.

The 70:100 ratio, which is 70 parts of water by weight to 100 parts of plaster by weight, is the ratio specified by USG Corporation for their USG No. 1 Pottery Plaster product. This is the standard casting plaster used in American ceramic studios. This ratio produces a mold with the right consistency and absorption rate for clay slip casting. Using more water makes a weaker, more porous mold that breaks down quickly under repeated casting. Using less water makes the mix set too fast and produces a dense mold that casts too slowly. The 70:100 ratio is the tested sweet spot for standard US casting clay formulas.

For standard deflocculated clay casting slips, the target specific gravity range is 1.75 to 1.80. This means the slip is 1.75 to 1.80 times heavier than an equal volume of water. Below 1.70 and the slip has too much water, which produces thin, fragile cast walls and very long casting times. Above 1.85 and the slip is too heavy. It may gel, pour unevenly, or fail to drain from the mold cleanly. Glaze slips operate on a different range entirely and are not governed by these same targets. Our Specific Gravity calculator tells you exactly where your slip falls and whether you need to add water or dry material to correct it.

Brongniart’s Formula is a 19th-century equation developed by Alexandre Brongniart, a French chemist and director of the Sevres porcelain factory. It calculates the dry weight of solid material suspended in a ceramic slip based on the slip’s volume, specific gravity, and the specific gravity of water. In practical terms it lets a studio potter calculate exactly how much dry clay material is in a given bucket of liquid slip, which is essential for adjusting recipes, calculating remaining material quantities, and troubleshooting casting problems. It remains the industry standard because it is accurate, simple, and works with any clay body without requiring specialized laboratory equipment.

You need three numbers: your kiln’s wattage rating from the metal data plate on the back or bottom of the kiln, the total hours your firing schedule runs, and your local electricity rate in cents per kWh. The basic formula is kilowatt-hours equals wattage divided by 1,000 multiplied by hours. Then multiply that figure by your kWh rate. Most electric kilns do not run at full wattage for the entire firing because they cycle their elements on and off as they ramp toward temperature. Our Kiln Firing Cost Calculator accounts for this by letting you input a duty cycle percentage or by using the standard average for electric kilns, which is roughly 40 to 60 percent of full wattage averaged across a complete firing session.

Based on 2024 EIA data, the states with the lowest average residential electricity rates are Louisiana at around 9.3 cents per kWh, Oklahoma at around 10.1 cents, and Arkansas and Tennessee in the 11-cent range. States in the Pacific Northwest like Oregon and Idaho also have historically low rates due to hydroelectric power, typically in the 10 to 12 cent range. The most expensive states are Hawaii at around 38 cents, California at around 25 cents, and Massachusetts at around 23 cents. For a studio running 100 kiln firings per year at a standard draw of 20 kWh per firing, a Louisiana potter might spend $186 annually on electricity while a Hawaii potter doing identical work pays over $760.

For casual hobby potting, probably not. The variation between bags of the same clay body from the same supplier is usually small enough to work from the published shrinkage rate and accept minor variation. For production work, especially if you are making functional ware with fitted lids, matching sets, or production runs where all pieces have to hit a specific size specification, you should fire a test tile from each new batch of clay. Some suppliers adjust their clay body formulation slightly between production runs, and even the same formula can shrink slightly differently depending on the moisture content of the bag when you receive it from the distributor.

Pyrometric cones are small pyramid-shaped ceramic pieces made by the Edward Orton Jr. Ceramic Foundation in Westerville, Ohio. They are made of specific ceramic formulas that melt and bend at precise temperature-and-time combinations inside a kiln. Potters place them in a kiln to verify the kiln actually reached the intended firing temperature. Cone numbers range from cone 022 (the lowest fire, about 1,087 degrees Fahrenheit) up through cone 14 (about 2,530 degrees Fahrenheit). Glaze recipes are designed to work at specific cone ranges. A cone 6 glaze will be properly melted and glossy at 2,232 degrees but may be completely underfired and powdery-looking at cone 04. Using a glaze outside its intended cone range is the most common cause of glaze failures in US studios.

No. Commercial glazes sold by Amaco, Spectrum, Coyote, or similar brands are proprietary premixed formulas sold ready to use out of the container. They do not have published recipes in parts or percentages. The Glaze Batch Scaler is designed for raw-material recipes that you are mixing yourself from dry ingredients like silica, feldspar, calcium carbonate (whiting), kaolin, and colorant oxides. If you are working from a recipe published in a ceramic chemistry textbook, from a studio instructor, or from community resources like Digitalfire or Glazy, our tool will convert it to gram weights for any batch size you need.

The electricity cost to run a kiln is essentially fixed for a given firing schedule. You are paying for a certain number of kilowatt-hours whether you fire 20 pieces or 80 pieces. This means your cost per piece drops in direct proportion as you load more pieces. A full kiln load always produces the lowest possible cost per piece. The Kiln Firing Cost Calculator shows this math explicitly via the per-piece cost breakdown. It is a powerful tool for justifying the discipline of waiting until a kiln is full before firing, rather than running partial loads out of impatience or convenience, which quietly eats into studio profitability over time.

If specific gravity is too low, below 1.70, you have too much water in the slip. The mold absorbs water from the slip to build up a clay wall, but dilute slip takes longer to build adequate wall thickness. Pieces come out thin and may crack when released from the mold. Fix: add dry material or let the bucket sit uncovered overnight so some water evaporates naturally. If specific gravity is too high, above 1.85, you have too much solid material in suspension. The slip may become thick and gel-like, refusing to flow into mold detail or drain properly after casting. Pieces may have uneven walls or a rough interior surface. Fix: add small amounts of water gradually and stir thoroughly, measuring specific gravity after each addition until you reach the target range.

Yes, with one important caveat: all ceramic calculations are only as accurate as the inputs you provide. The shrinkage calculator is only as accurate as the test tile measurements you take. The kiln cost calculator is only as accurate as your kiln’s actual wattage rating and firing schedule. The glaze batch calculator is precise to within the accuracy of your gram scale, which should be accurate to at least 0.1 grams for small batches. All the formulas used in these tools are standard industry calculations used in production ceramic facilities. They are the same math used by ceramic engineers at commercial factories, wrapped in a more accessible interface for studio use rather than an industrial computer system.

Regional preference comes from a combination of history, logistics, and studio culture. Certain clay deposits historically existed near certain cities, making locally-sourced clays cheaper to ship and more common in local studios. Today, regional distributors carry certain brands by default. Highwater Clays is based in Asheville, North Carolina and has a strong following in the Southeast. Laguna Clay Company is headquartered in City of Industry, California and dominates the West Coast market. Sheffield Pottery in Massachusetts is a major East Coast supplier. The shrinkage rates and working properties vary noticeably between these suppliers’ clay bodies, which is exactly why this hub includes brand-specific presets rather than just generic type averages that may not match your actual clay bag.

Yes. Every calculator in this hub includes a WhatsApp share button that constructs a pre-written message containing your key inputs and results. It opens WhatsApp in a new tab with the message pre-filled so you can send it to anyone in your contact list. Every tool also includes a PDF export button that generates a cleanly formatted report with all inputs, outputs, and the calculation method used. This is useful for studio teaching, keeping firing records, or documenting a glaze batch for quality control if you are supplying glazed pieces to a gallery or wholesale buyer who needs material documentation for their purchasing records.