Tolerance & Fits Calculator

The Tolerance & Fits Calculator is an interactive ISO 286 limits and fits tool that computes hole and shaft tolerances, determines fit type (clearance, transition, or interference), and visualizes the assembly relationship. When a shaft is inserted into a hole, the difference between their manufactured sizes determines whether the fit allows free movement, requires force to assemble, or falls somewhere in between. This calculator handles all the complex lookup tables and calculations automatically.

You can specify any combination of basic size (1-500 mm), hole tolerance designation (letter + IT grade), and shaft tolerance designation (letter + IT grade). Nine common fit presets are available (from loose running H11/c11 to drive fit H7/s6). The interactive canvas shows a cross-section of the hole and shaft assembly with colour-coded tolerance bands, and you can even drag the shaft in and out to visualize the fit relationship.

The calculator opens in Explore mode with a split layout: the canvas on the left showing the hole-shaft cross-section, and the sidebar on the right with fit selectors, presets, and results. The canvas displays the tolerance bands for both the hole and shaft with exaggerated scale so you can clearly see the gap or overlap.

To explore a fit: (1) Enter a basic size (e.g., 50 mm). (2) Select the hole designation using the letter and grade dropdowns (e.g., H7). (3) Select the shaft designation (e.g., g6). Or simply click one of the nine preset buttons (Loose Running, Free Running, Close Running, Sliding, Locational, Transition, Interference, Press, Drive). (4) Read the results: hole limits, shaft limits, tolerances, deviations, and fit analysis (max/min clearance or interference). (5) Open the step-by-step calculation panel to see how each value is derived.

The Learn mode (equivalent to Simulate) provides a guided tutorial through limits and fits concepts. Navigate through lesson slides using Prev/Next buttons. Topics cover: what is a tolerance, what is a fit, the three types of fits, how the ISO 286 system works (basic size, IT grades, fundamental deviations), hole basis vs. shaft basis systems, and how to read a fit designation like H7/g6.

Each slide includes clear explanations with the canvas updating to illustrate the current concept. The progression builds from basic definitions to the full calculation procedure, giving you a structured learning path through this important engineering topic.

Explore mode is the main workspace. The canvas renders the hole and shaft cross-section with tolerance bands colour-coded: hole in one colour, shaft in another. The gap (clearance) or overlap (interference) between them is clearly visible. Use the "Slide In" and "Slide Out" buttons or drag the shaft to animate the assembly and see how the parts interact.

The results grid shows three cards: Hole (max limit, min limit, tolerance, ES, EI), Shaft (max limit, min limit, tolerance, es, ei), and Fit Analysis (max clearance/interference, min clearance/interference). The step-by-step calculation panel walks through every step: identifying the size range, looking up the IT tolerance value, determining the fundamental deviation from the letter code, calculating upper and lower deviations, and computing the final limits. This is exactly the procedure you would follow in an exam.

Practice mode presents a random fit designation (e.g., diameter 30 H7/k6) and asks you to calculate hole max, hole min, shaft max, shaft min limits, and identify the fit type. Enter your values to three decimal places and select the fit type from a dropdown. Click "Check" to verify your answers. The solution panel reveals the complete step-by-step calculation if you need help. Your running score tracks performance.

Quiz mode runs five questions combining fit type identification and limit calculations. After five questions, you see your score with a star rating and a review of each answer. New questions use different sizes and designations each time, ensuring comprehensive coverage of the ISO 286 system.

• Start with the nine presets to develop intuition for how different fits look. Notice how clearance fits have visible gaps while interference fits show overlap.
• Memorise the key designations: H = hole with zero lower deviation, h = shaft with zero upper deviation. Letters before H/h in the alphabet produce clearance fits; letters after produce interference.
• IT grades determine tolerance magnitude: IT5-IT6 are precision grades, IT7 is general purpose, IT8-IT11 are for looser fits.
• H7/g6 (sliding fit) is the most commonly referenced fit in engineering exams. Know its calculation procedure inside out.
• To quickly determine fit type: if the maximum shaft size is less than the minimum hole size, it is always clearance. If the minimum shaft size is greater than the maximum hole size, it is always interference. Otherwise, it is transition.
• Use the step-by-step calculation panel in Explore mode as a reference when working Practice problems. Over time, you will memorise the procedure.
• Practice problems with different size ranges (e.g., 18-30, 30-50, 50-80) since the IT values change between ranges.