Convert 1 1/8 Inches to MM - Accurate Calculator
Convert 1 1/8" to millimeters with high precision
Results at Different Precisions
🔧 DIY & Hardware
For hardware and DIY projects, 1 1/8" equals 28.58 mm, which is essential when working with metric tools or international specifications.
⚙️ Engineering & Manufacturing
In engineering contexts, 1 1/8" converts to 28.575000 mm with high precision for accurate technical specifications.
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Exact answer, measurement guidance, and nearby sizes
Direct answer and formula
1 1/8 inches is 28.575 mm exactly because the international inch is exactly 25.4 mm.
1 1/8 × 25.4 = 28.575 mm
Basis: 1 inch = 25.4 mm exactly (international inch definition)
Rounding, fractions, and tolerance
The converted value 28.575 mm is exact. To one decimal it is 28.6 mm; the nearest 0.5 mm is 28.5 mm (difference 0.075 mm), and the nearest whole millimeter is 29 mm (difference 0.425 mm). Rounded metric sizes are not interchangeable unless that difference fits the tolerance budget.
A nearby rounded size is acceptable only when its absolute difference is within the documented dimensional tolerance and all non-dimensional compatibility checks pass.
Woodworking cut transfer
An inch plan dimension is being transferred to a metric saw fence or measuring tool. For this route, 1 1/8 inches converts to 28.575 mm. Use a common reference edge and choose rounding that stays inside the cut allowance.
- Use a common reference edge and choose rounding that stays inside the cut allowance.
- Kerf, squareness, and stock condition still affect the finished part.
Illustrative measurement workflow; it does not claim that this value is a standard product size.
Editorial measurement check
If the value came from a drawing, carry its tolerance and revision context alongside the converted unit.
A nearby catalog or tool size is only a candidate for review; numerical proximity does not establish interchangeability.
Verify the final setting with the instrument or template used in the real workflow before releasing the dimension.
Nearby comparison and substitution boundary
Nearest-0.5-mm rounding maps exact results from 28.25 mm up to (but not including) 28.75 mm to 28.5 mm with half-up ties. Using 28.5 mm as a physical substitute changes this dimension by 0.075 mm; verify fit, thread, clearance, or process allowance as applicable.
Candidate: 28.5 mm; absolute difference: 0.075 mm.
Questions about this exact conversion
How do you convert 1 1/8 inches?
1 1/8 inches is 28.575 mm exactly because the international inch is exactly 25.4 mm.
How many digits should be kept for 1 1/8 inches?
The converted value 28.575 mm is exact. To one decimal it is 28.6 mm; the nearest 0.5 mm is 28.5 mm (difference 0.075 mm), and the nearest whole millimeter is 29 mm (difference 0.425 mm). Rounded metric sizes are not interchangeable unless that difference fits the tolerance budget.
What should be checked in this woodworking cut transfer example?
Use a common reference edge and choose rounding that stays inside the cut allowance. Kerf, squareness, and stock condition still affect the finished part.
Can 28.5 mm replace 1 1/8 inches?
Nearest-0.5-mm rounding maps exact results from 28.25 mm up to (but not including) 28.75 mm to 28.5 mm with half-up ties. Using 28.5 mm as a physical substitute changes this dimension by 0.075 mm; verify fit, thread, clearance, or process allowance as applicable.