← AskMachinist · Guides · Calculator · 🔎 Search

How to Check Calipers with Gage Blocks

Guide · Updated October 27, 2026

Calipers get dropped, the jaws wear near the tips and dial racks pick up chips, so a caliper that zeros fine can still read off at 4 or 6 inches. A handful of gage blocks shows you in a few minutes. Below are practical test sizes for a 6 in and a 150 mm caliper, with the fewest-block stack for each from the same solver the free gage block stack calculator uses.

Before you start

• Let the caliper and blocks sit together so they are at the same temperature; handle blocks by the edges. See the temperature correction calculator for how much heat matters on long stacks.
• Wipe the jaws, slide and depth rod. Close the jaws and zero (digital) or set the bezel (dial).
• Hold the jaws light and square on the blocks; use the thumb roller the same way every time. Measure near the jaw base, then again near the tips, since tip wear is common.
• Wring two-block stacks properly: see how to wring gage blocks.

6 in caliper: outside test sizes (81-piece inch set)

Tap a size to open it in the calculator. Print this page and write readings in the last column.

150 mm caliper: outside test sizes (88-piece metric set)

Have an 8, 12 in or 300 mm caliper? Add the long blocks from your set (or a long-block set) and build each size in the calculator, which picks the fewest blocks you own.

Inside, depth and step checks

• Inside jaws: wring a stack between gage block accessory jaws, or check against a ring gage. A quick shop check is to set a micrometer to a size and measure it with the inside jaws.
• Depth rod: stand two equal blocks on a surface plate, rest the caliper end across them and run the rod down to the plate; the reading should equal the block height.
• Step: set a block on the plate and read the step between the plate and the block top with the back of the slide.

Reading the results

• Take each size two or three times and note the average.
• Same error at every size usually means zero is off. Error that grows along the beam points to a bent beam or worn rack; error only at the tips means worn jaws.
• Compare against the caliper's stated accuracy. For tighter tolerances, move to a micrometer: see how to check a micrometer with gage blocks, or for height work, how to check a height gage, or a dial indicator.

Buying blocks for this? Read how to choose a gage block set and gage block grades explained; workshop grade is plenty for caliper checks.

Tools that help

• 81-piece inch gage block sets: cover every inch size above.
• Gage block accessory sets: jaws and holders for inside checks.
• Granite surface plates: a flat reference for depth and step checks.

See also: How to zero a digital caliper and micrometer, How to read a vernier scale.

See also: How to Use a Dial Caliper.

FAQ

What sizes should I use to check a 6 inch caliper?

Spread checks across the range, for example 0.125, 0.500, 1.000, 2.000, 3.000, 4.000, 5.000 and 6.000 in. From an 81-piece set, 5.000 in = 4.000 + 1.000 and 6.000 in = 4.000 + 2.000.

Can I check the inside jaws of a caliper with gage blocks?

Yes, with gage block accessories: wring a stack between two jaw or holder pieces to make an inside size, or check against a ring gage. Without accessories, compare inside jaws to a micrometer set at a known size.

How accurate should a caliper be?

Most 6 in / 150 mm digital and dial calipers are stated around plus or minus 0.001 in (0.02-0.03 mm). Use the accuracy on your caliper's spec sheet and your shop's acceptance limit.

As an Amazon Associate I earn from qualifying purchases; links marked "sponsored" may earn a commission at no cost to you. Prices and availability change; check each listing before buying. This guide is general information; follow your shop's calibration procedure and the caliper maker's instructions.

Need a stack for another size? Use the free gage block stack calculator (no login). Have a shop question? Ask a machinist or browse all guides.