Planar geometry — no pressure/load calculation
Bolt Circle Geometry and Coordinates
Calculate spacing and centre coordinates for equally spaced holes on a true bolt circle. Enter the dimensions and orientation from your drawing.
Geometric results
| Hole | Angolo (°) | X | y |
|---|
Equally spaced circle geometry
Let D be the bolt-circle diameter,R=D/2,n the number of equally spaced centres,and θ0 the first-hole angle. The central angle between adjacent centres is Δθ=360°/n=2π/n radians. Bisecting the isosceles triangle formed by two adjacent radii gives half-chord R·sin(π/n),therefore the full chord is 2R·sin(π/n)=D·sin(π/n).
chord = D·sin(π/n) · arc pitch = πD/n
For hole k=1…n,with index j=k−1,the angle is θj=θ0+s·j·360°/n,where s=+1 counter-clockwise or−1 clockwise. Coordinates relative to the bolt-circle centre are xj=R cos θj,yj=R sin θj. The adjacent clear gap is chord−dh; a negative value means the entered circular holes geometrically overlap. Outer and inner radial envelopes are D+dh and D−dh; they are geometry,not required flange diameters.
Units and numerical scope
All length inputs and outputs use the selected unit consistently. The inch is exactly25.4mm according to NIST. Thus a physically identical pattern entered as254mm or10in produces outputs that differ by exactly25.4 in numerical scale. The computational bounds (positive lengths≤10⁹ selected units,n=2…360,|θ0|≤10⁹°) prevent non-finite or impractically large browser calculations; they are not standards limits.
Standards context — none is implemented here
ASME PCC-1—2022 is an assembly guideline for pressure-boundary bolted flange joints within its stated scope; it is not the source of the elementary circle formulas above. ASME B16.5—2025 covers specified pressure-temperature ratings,materials,dimensions,tolerances,marking and testing for its listed standard flanges; this page does not reproduce its tables.
BS EN1591-1:2024 is the current calculation standard for structural integrity and leak tightness of gasketed circular flange joints using gasket parameters tied to EN13555:2021. Its joint model is not the former page’s two-term load estimate and is not implemented here.
Do not use these geometric outputs as bolt load or preload. The former calculator ignored its gasket-y input,omitted seating load and effective-gasket-geometry rules,and labelled a simplified estimate as PCC-1/EN1591. Those load calculations were removed because the necessary licensed procedure and design inputs were absent.
Sources: official ASME PCC-1—2022 and B16.5—2025 records;BSI current BS EN1591-1:2024 scope/history;and NIST length-unit definition. Checked12July2026. No closed clause,table or coefficient is asserted.
