← AskMachinist · Guides · Calculator · 🔎 Search
Gage Block Warm-Up and Thermal Soak
Guide · Updated October 27, 2026
Steel grows about 6.4 millionths of an inch per inch per °F. A block warmed by your hand can grow tenths, so careful work means letting the blocks and part soak to the same temperature.
Need an exact reference size?
Build any gage block stack with the free Gage Block Calculator. Free, no login.
Step by step
- Measure room temperature: Put a shop thermometer near the plate. The reference temperature is 68 °F (20 °C).
- Soak: Leave blocks and the part on the plate together until they're the same temperature. Allow more time for bigger parts.
- Handle less: Use gloves, tongs or insulated pads and keep your hands off the stack.
- Wait after wringing: Give a hand-warmed stack time to cool before measuring.
- Compensate if needed: If you can't hold 68 °F, correct for the temperature difference.
Rules of thumb
- Steel: about 6.4 µin/in/°F.
- A 4 in stack warmed 5 °F grows about 0.00013 in.
- More detail: temperature compensation.
Related: temperature compensation, wringing.
Worked example: how much a warm block grows
Gage block lengths are defined at 20 °C (68 °F). Steel blocks grow about 11.5 µm per meter per °C, or about 6.4 µin per inch per °F. A 4.000 in steel block handled until it reaches 78 °F, 10 °F above standard, grows 4 × 6.4 × 10 = 256 µin, about 0.00026 in. That is larger than the Grade 0 tolerance for that size, so a warm stack can put a calibration out of spec.
Ceramic blocks expand at about 9.3 µm/m/°C, closer to steel parts, so the correction is similar. For an accurate check, let blocks and parts soak on the same plate for an hour or more per inch of thickness, handle them with gloves or tongs, and record room temperature. If the part and block are the same material at the same temperature, the error largely cancels, which is why soaking together matters more than the room temperature itself.
FAQ
How long should gage blocks soak?
Until they match the part and the room. Larger blocks and parts need longer, so many shops wait an hour or more for precision work.
Why does handling matter?
Hand heat expands steel, about 6.4 µin per inch per °F.
What is the reference temperature?
68 °F (20 °C), per ISO 1.
How do I correct a stack?
Use the expansion coefficient. Build any reference size free with the Gage Block Calculator at gageblockcalc.com.
Related guides and calculators
- How to build a gage block stack
- How to wring gage blocks
- How to choose a gage block set
- Gage block care and wear blocks
- Carbide vs steel vs ceramic gage blocks
- How to check a height gage with gage blocks
- Machinist Christmas gift guide
- How to Use a Surface Plate
- How to Shrink Fit a Part (Heating Temperature and Method)
- Thermal Expansion Correction for Precision Measurement
- All free machinist calculators
Build your stack in seconds
The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.
Questions? Ask a machinist.
General shop information only — follow your gage manufacturer's instructions and your quality system.