What this calculator does
Every FDM print is built as a stack of layers, and the layer height setting decides how many of them a given model needs. A taller model or a finer layer height both mean more layers, which is the main lever for the trade-off between print time and surface detail.
A separate but related question is how many of those layers need to be fully solid on the top and bottom surfaces, rather than following the infill pattern. Slicers convert a target shell thickness into a whole number of solid layers, rounding up so the shell is never thinner than requested.
The formula
Divide the model height by the layer height to get the total layer count. Divide the target shell thickness by the same layer height and round up to get the number of solid top/bottom layers.
| Term | Meaning |
|---|---|
| Layer height | The vertical thickness of each printed layer, a core slicer setting that trades detail against print time. |
| Layer count | The total number of layers the printer will lay down over the full model height. |
| Solid layers | The whole number of layers needed, at the current layer height, to reach the target top or bottom shell thickness. |
The inputs explained
| Field | What to enter |
|---|---|
| Model height (mm) | The total height of the model as it will sit on the print bed. |
| Layer height (mm) | The layer height set in the slicer for this print. |
| Target top/bottom shell thickness (mm) | The minimum top/bottom shell thickness you want, regardless of infill percentage. |
When to use it
Choosing a layer height for a tall print
A taller model at a very fine layer height can mean thousands of layers and a very long print; checking the layer count first shows whether a coarser setting is worth considering.
Setting top/bottom shell thickness in the slicer
Most slicers ask for a shell thickness in millimetres and convert it to a layer count internally; working that out here shows exactly what number of layers you are actually getting.
Matching detail to a specific layer height
Comparing layer counts across a few layer height options is a quick way to see how much finer detail costs in additional layers.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How layer count changes with layer height, at a fixed model height
A fixed 60 mm tall model, across a range of layer heights.
How solid layers needed changes with layer height, at a fixed shell thickness
A fixed 1.2 mm shell target, across a range of layer heights.
Questions
Why does the actual shell thickness sometimes come out slightly more than what I asked for?
Because solid layers must be a whole number, and the calculation rounds up rather than down. A 1.2 mm target at a 0.2 mm layer height needs exactly 6 layers, but a 1.25 mm target still rounds up to 7, giving 1.4 mm of actual shell.
Does layer count affect strength as well as appearance?
Indirectly. Layer height affects how well layers bond to each other and the visible surface finish, but overall strength is driven more by wall count, infill and material choice than by layer count on its own.
What layer height should I use?
It depends on the trade-off you want between print time and surface detail; there is no single correct value. A finer layer height improves visible detail and reduces layer-line stepping on curved surfaces, at the cost of more layers and a longer print.
Is top and bottom shell thickness the same as wall thickness?
No. Wall (perimeter) thickness is the vertical, outward-facing shell around the sides of the model. Top/bottom shell thickness is the horizontal solid layers capping the model above and below any infill.
To see how much of the model volume that infill and shell actually take up, use the infill volume calculator. For a time estimate once the layer count is set, see the print time estimate calculator.