A full cone comes to a single point (apex).
Dimensions
Layout Options
The calculator works out the flat pattern. You do not need to enter plate length.
Cone Development Preview
Enter the cone dimensions and calculate to generate the flat pattern, sector angle, arc lengths, split sections and radial line layout.
Full Cone
Truncated / Reducer
Flat Pattern Sector
Cone Pattern Marking Guide
- Mark the apex / centre point on your plate.
- Mark the outer pattern radius and draw the full arc.
- For truncated cones, mark the inner pattern radius and draw the inner arc.
- Measure and mark the sector angle (or section angle if split).
- Divide the sector into the calculated radial line spacing.
- Step out the outer arc spacing along the outside edge with dividers.
- If truncated, step out the inner arc spacing along the inside edge.
- Connect the points back to the apex to draw the radial bend lines.
- If split into sections, repeat the same layout for each section.
- Add seam allowance, trimming allowance and weld prep as required outside the calculated pattern.
When to Split a Cone Pattern
Large cone patterns may be too big to cut, roll, press or handle in one piece. They may also exceed the standard plate sizes available in your workshop. Splitting the pattern into two halves or more sections can make fabrication significantly easier.
Small cones, single seam
Medium cones, two seams
Large hoppers/tanks, four seams
User-defined equal sections
Each split section needs its own seam allowance if welded separately.
Cone Fabrication Notes
- A full cone comes to a point, while a truncated cone/reducer has a large diameter and a small diameter.
- Vertical height is not the same as slant height. Ensure you measure straight down the centre line.
- The flat pattern is a sector shape (a slice of a circle), not a rectangle.
- Always allow for seam gaps, weld preparation, trimming and forming allowances outside the calculator's pure geometric pattern.
- Material thickness and the rolling/pressing method can affect the final fit. For thick plate, use the Mean Diameter.
Common Development Mistakes
- Confusing vertical height with slant height when entering dimensions.
- Using the wrong diameter type (Outside vs Inside) without adjusting for thickness.
- Making bend line spacing too small, resulting in too many bends that cannot fit in a press brake die.
- Not allowing extra material for trimming the flat spots left by plate rollers.
- Confusing side view dimensions with flat pattern dimensions when drawing out the plate.
Frequently Asked Questions
Disclaimer: This cone calculator provides flat pattern development and fabrication estimating guidance only. Final pattern allowance, seam preparation, rolling or pressing method, trimming, weld shrinkage, fit-up, material grade and workshop procedure must be checked by a qualified fabricator, boilermaker or engineer.
Calculation method, worked example and reference
What this calculator does and formula: Cone volume V = πr²h/3; curved surface area = πr√(r²+h²); total area adds πr².
Variables and units: Enter values in the units named by the controls. The calculator converts through its internal base unit or applies the displayed geometric or financial relationship before rounding the presented result.
Verified worked example: For radius 2 m and height 3 m, V = π×2²×3/3 = 12.5664 m³.
Result interpretation, assumptions and practical limits: Use consistent linear units. This is ideal geometry and excludes wall thickness, truncation, seams and fabrication allowances.
Professional check: Treat the result as a planning estimate. Where safety, regulated work, contracts or significant money are involved, verify inputs and the result with the governing standard, manufacturer data and an appropriately qualified professional.
Authoritative reference
Cone and flat-pattern geometry
Use this schematic to identify the calculator inputs and how they relate. It is explanatory and not a fabrication, installation or lift-plan drawing.