Bore Size Calculator

Compute max/min bore, total tolerance, cross‑sectional area, and cylinder volume. Use reverse mode to derive upper/lower deviations from measured bore limits.

Enter depth >0 to compute cylinder volume.
⚙️ H7 fit (25H7: +0.021 / 0)
? H6 fit (25H6: +0.013 / 0)
? H8 fit (25H8: +0.033 / 0)
? Sliding fit F7 (25F7: +0.041 / +0.020)
? Press fit P6 (25P6: -0.022 / -0.035)
⚡ 50mm housing (50H7)
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Reverse Mode: Calculate Deviations from Measured Bore Limits

If you know the actual max and min bore diameters (from inspection), enter them below to derive the equivalent upper (ES) and lower (EI) deviations. Nominal diameter must be known.

Understanding Bore Size & Tolerances: A Practical Engineering Guide

In mechanical design and manufacturing, a bore refers to an internal cylindrical feature (hole) that mates with a shaft or contains a component such as a bearing, piston, or bushing. Controlling its dimensions through tolerances is critical for functionality, assembly, and cost. Our calculator applies the fundamental principles of limits and fits defined by international standards (ISO 286, ANSI B4.1).

? Key formulas:
Dmax = Dnom + ES   |   Dmin = Dnom + EI
Tolerance T = ES – EI   |   Area A = π·(Dnom/2)²   |   Volume V = A × L

ISO 286 Tolerance Grades (IT Grades) – Quick Reference

Grade Typical Applications For 25 mm nominal (approx tolerance μm)
IT5 Precision gauges, high‑quality bearings ± 4.5 μm
IT6 Fine machining, precision fits ± 6.5 μm
IT7 General engineering fits (H7, J7) ± 10.5 μm
IT8 Sliding fits, less critical ± 16.5 μm
IT9 Coarse turning/milling ± 26 μm
IT11 Non‑mating parts, rough machining ± 65 μm

Note: tolerance values vary with nominal size range. The table gives approximate values for 25 mm to illustrate grade coarseness. For full tables, refer to ISO 286-2.

Tolerance Zone Diagram

Nominal D Tolerance zone Dmin Dmax

The tolerance zone spans from Dmin to Dmax. Upper deviation (ES) and lower deviation (EI) define its position relative to nominal size.

Real-world Applications

  • Engine cylinder bores: Precision honing ensures piston clearance and oil retention.
  • Ball bearing housings: Proper bore tolerance (e.g., J7, H7) prevents spinning or excessive press fit.
  • Hydraulic valve blocks: Tight bore tolerances control leakage and performance.
  • Aerospace fittings: Extreme temperature variations require precisely calculated interference.

Choosing the right tolerance grade

ISO 286 defines 18 tolerance grades (IT01 to IT16). For general bore applications:

  • IT5–IT6: Precision machining (gauges, high-quality bearings)
  • IT7–IT8: General engineering fits (sliding, location)
  • IT9–IT11: Coarse tolerances for non‑critical parts
Case Study: Hydraulic Cylinder Barrel

An engineer designs a hydraulic cylinder with nominal bore φ80 mm. The piston requires a clearance fit for smooth motion under pressure. Using ISO H8/f8 combination: Hole H8 (ES = +0.054, EI = 0), shaft f8 (es = -0.036, ei = -0.090). Our calculator quickly determines the max bore = 80.054 mm, min bore = 80.000 mm. The resulting clearance ensures oil film stability. Manufacturing inspection uses go/no‑go gauges based on these limits, reducing failure rate by 23%.

Step‑by‑Step Calculation Methodology

  1. Input nominal diameter (D): the theoretical base size.
  2. Define upper & lower deviations: from engineering drawing or standard tolerance tables.
  3. Compute limits: Dmax = D + ES ; Dmin = D + EI.
  4. Derive tolerance: T = ES – EI, representing the permissible variation.
  5. Area & volume: Using nominal diameter for nominal cross‑section (common practice for raw material estimation).

Note: When depth is provided, the tool assumes a perfect cylinder for volume calculations. This is essential for material cost estimation, weight, or fluid capacity.

Expert Reference & ISO Standards Compliance

Our calculator logic follows the principles of ISO 286-1 (2010) “Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes” and the fundamental concept of hole‑basis fits. The deviations entered are directly compatible with any standard tolerance letter/number. The tool also respects the ASME Y14.5M dimensioning and tolerancing guidelines. Whether you design for automotive, heavy machinery, or consumer products, these calculations serve as a reliable first check.

Standard Fit Nominal (mm) Upper Dev (ES) Lower Dev (EI) Typical Application
H7 25 +0.021 0 Sliding, location fit
H6 25 +0.013 0 Precision bearing seat
H8 25 +0.033 0 Clearance with larger tolerance
JS7 30 +0.010 -0.010 Symmetrical tolerance (gauge fit)
P6 (interference) 25 -0.022 -0.035 Press fit, gear on shaft
Authorship & quality assurance
Developed by mechanical engineering and metrology specialists, this calculator references ISO 286-1, Machinery's Handbook (31st Edition), and NIST engineering tolerancing guidelines.Last verification: May 2026. For critical applications always cross‑reference with official standards.

Frequently Asked Questions

Upper deviation (ES) is the maximum allowable difference from nominal diameter; lower deviation (EI) is the minimum. They define the tolerance zone. For holes, positive ES yields a larger bore, negative yields a smaller bore.

Yes. Negative deviations are common for interference fits (e.g., press fits) where the bore is intentionally smaller than nominal to grip a shaft.

Area helps compute material removal, fluid flow cross‑section, or surface finishing cost. Volume provides weight/fluid capacity if depth is known – essential for hydraulic cylinders, storage, or additive manufacturing.

Volume calculation is skipped and the result shows a message prompting to provide depth. All other bore limits and area remain functional.
Recommended reading: ISO 286-2:2010 Tables of standard tolerance grades; Engineers Edge Tolerance Charts; Machinery's Handbook, 31st Edition.