Firing

Kiln Loading Calculator

Calculate how many pieces fit on each shelf and in the total kiln based on kiln interior dimensions, shelf height, and piece size.

Updated May 2026

Kiln Interior Dimensions

Interior Length (cm)

Interior Width (cm)

Interior Height (cm)

Shelf Thickness (mm)

Post Height (cm)

Common: 5, 7, 10, 15cm.

Piece Dimensions

Piece Height (cm)

Piece Diameter / Width (cm)

Piece Shape

Bottom Clearance (cm)

Space below first shelf (usually 4–6cm).

Safety Clearance Above Piece (cm)

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Results

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Enter your measurements above and click Calculate.

How Kiln Loading Works

Efficient kiln loading maximises the number of pieces fired per kilowatt-hour while maintaining even heat distribution. The key variables are shelf area, post height, and piece footprint.

The Calculation

Pieces per shelf = (Shelf area × Packing efficiency) / Piece footprint

Slot height = Post height + Shelf thickness + Piece height + Safety clearance
Number of shelves = (Kiln height − Bottom gap) / Slot height
Total pieces = Pieces per shelf × Number of shelves

Packing Efficiency

Round pieces can never perfectly tile a flat shelf. Hexagonal packing of circles gives a theoretical maximum of ~90%, but in practice with uneven footprints and glaze spacing, 70–75% is realistic for round ware. Square tiles and boxes pack at ~85–88%.

Common Post Heights

Post Height	Best For
2–3 cm	Tiles, small flat pieces, bisque stacking
5–7 cm	Cups, small bowls, mugs
10 cm	Standard mugs, medium bowls
15 cm	Tall cylinders, pitchers
20+ cm	Large vases, storage jars

Heat Distribution Tips

Leave 2–5cm between the bottom shelf and kiln floor for even heat distribution.
In top-loading kilns, the top shelf may fire slightly hotter — place your most durable pieces there.
Always leave at least 1cm between glazed surfaces in glaze firings.
Bisque firings allow pieces to touch or even be stacked (rim to rim for bowls).

lightbulb Quick Tips

check_circle Load the heaviest, tallest pieces on the bottom shelf — they're closest to the elements and benefit from the most even heat in a top-loading kiln.
check_circle Mix short and tall posts across different levels to fill the kiln height efficiently — you're not limited to one post height per firing.
check_circle In glaze firings, use kiln wash on shelves and leave 1–2cm between pieces. In bisque firings, you can stack pieces rim-to-rim to nearly double your load.
check_circle Keep a loading sketch or photo for each firing — when you get a beautiful result, you'll want to know exactly where in the kiln it came from.

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Frequently Asked Questions

How do I measure kiln interior dimensions? expand_more

Measure inside the firebrick walls, not the outer cabinet. For round kilns, measure the usable diameter where shelves sit. For front-loaders, measure the usable width, depth, and height from the floor to the element at the top.

What post height should I use? expand_more

Use the shortest post that gives safe clearance above your tallest piece (minimum 1–2cm). Common heights are 5, 7, 10, and 15cm. Mixing posts to customise levels is standard practice.

Should I leave space between pieces? expand_more

For bisque firings, pieces can touch (though stacking should be stable). For glaze firings, maintain at least 1cm between glazed surfaces to prevent pieces fusing together. The calculator uses a packing efficiency factor to account for this.

Can the top shelf have a different post height? expand_more

Yes, in practice you mix post heights. This calculator assumes uniform post height for the estimate. For a precise count with mixed heights, calculate each level separately.