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 | Angle (°) | 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.
Nikolai Shelkovenko
Nikolai Shelkovenko is a vibration analysis engineer and the founder and CEO of Vibromera. For more than 15 years he has balanced rotating equipment in the field rather than on a test bench: mulchers, industrial fans, crushers, centrifuges, shafts and spindles. That work is what the Balanset instruments grew out of — they were designed as a tool a specialist can carry to the machine and use alone, on site, not as laboratory equipment. Vibromera was founded in 2017 and has been based in Porto, Portugal, since 2023. Development, assembly and support of the Balanset line all happen here. The flagship instrument is the Balanset-1A, a portable analyser for single- and two-plane balancing and for vibration diagnostics. Nikolai is personally involved in customer support, in working through difficult balancing cases and in the development of the software. He works with customers worldwide, in any language.
