Depth Gauge vs Depth Micrometer: How to Choose One From Your Tolerance (and Which Mitutoyo Fits)

A depth gauge measures how far a hole, counterbore, slot or step goes below the surface it sits on. Which one you need depends on the tolerance on the drawing, whether the gauge will see coolant, and how wide the opening is. This guide explains the types (vernier, dial, digital, depth micrometer), shows how to pick one from the tolerance you have to hold, and compares the 23 Mitutoyo depth gauges and depth micrometers we ship from Japan.

Quick picks

Mitutoyo VDS-15AX digital depth gauge 0-150 mm Most shop work VDS-15AX (571-201-30)

0–150 mm, 0.01 mm display, ±0.02 mm, data output.

View VDS-15AX
Mitutoyo VDS-P15 coolant-proof IP67 depth gauge Coolant on the machine VDS-P15 (571-251-20)

Coolant-proof IP67, 0–150 mm, ±0.02 mm, data output.

View VDS-P15
Mitutoyo DMS60-25 depth micrometer 0-25 mm Tight tolerances DMS60-25 (128-101)

Depth micrometer, 0–25 mm, ±0.003 mm, ratchet (constant-pressure device).

View DMS60-25
Mitutoyo 7211A dial depth gauge No battery, light force 7211A dial depth gauge

±0.015 mm, measuring force 1.4 N or less, 63.5 mm base.

View 7211A
Mitutoyo NTD35-M digital tire depth gauge Tire tread (automotive) NTD35-M (571-100-20)

0–25 mm, 0.01 mm display, ±0.02 mm, 60 mm base.

View NTD35-M
Mitutoyo VDS-15 vernier depth gauge 150 mm Vernier, no electronics VDS-15 (527-201)

0–150 mm, 0.05 mm graduation, ±0.05 mm.

View VDS-15
Quick answer
  • Start from your tolerance, not the display. A common shop rule (the 10:1 rule) is that the instrument's error should be no more than one tenth of the part tolerance; today a 4:1 ratio is the more common minimum (MSC Industrial). The comparison table below shows, for each model, the tightest tolerance it can check under both ratios.
  • Counterbores, slots and pockets at about ±0.1 mm or looser (check your drawing; precision joints can be tighter): a 150 mm digital depth gauge such as the VDS-15AX, or the IP67 VDS-P15 if it lives near coolant.
  • Tolerances tighter than about ±0.08 mm (down to about ±0.012 mm at 4:1): a depth micrometer (DMS60-25, or the digital DMC100-150MX).
  • Deep features (300–600 mm): VDS-30AX, VDS-P30 or VDS-60DC.
  • Can you just use the depth rod on your caliper? For occasional, loose checks, yes. For repeated or critical depths, a gauge with a wide base is easier to keep square (see the FAQ).

Depth gauge types: vernier, dial, digital and depth micrometer

All depth gauges work the same way: a flat base sits across the surface around the feature, and a rod or blade goes down to the bottom. The reading is the distance from the base face to the rod tip. What changes is how you read it and how small an error the instrument is rated for.

  • Vernier depth gauge (Mitutoyo VDS-15/20/30/60, series 527): scale on the blade, vernier on the base. No battery. On our models the graduation is 0.05 mm and the maximum permissible error is ±0.05 to ±0.10 mm depending on length (product pages).
  • Dial depth gauge (7211A–7220A): a dial indicator mounted in a base. The reading is on a dial, so there is no vernier to interpret and no battery. Our models list 0.01 mm graduation and ±0.015 or ±0.030 mm (product pages).
  • Digital depth gauge (VDS-AX and VDS-P series 571, NTD35-M): an LCD with a 0.01 mm display, ±0.02 to ±0.05 mm on our models, data output on most, and IP67 coolant protection on the VDS-P series (product pages; Mitutoyo 571 series catalog).
  • Depth micrometer (DMS, DMC): a micrometer head on a base. Our models list ±0.003 mm and a constant-pressure device (ratchet) on the mechanical DMS models (product pages). AIMS Industrial describes the depth micrometer as the step up when a depth gauge cannot hold the tolerance.

How to choose a depth gauge

1. Work back from the tolerance

Resolution is what the display shows; the maximum permissible error (MPE) is how far the reading may be from the true depth. Every product page below lists the MPE, and that is the figure to compare. MSC Industrial traces the 10:1 rule to MIL-STD-120 (1950): the measuring equipment's accuracy should not exceed 10% of the part tolerance. MSC also notes that the requirement is now usually stated as a 4:1 test accuracy ratio (25% of tolerance). We use both in the table: tightest tolerance at 10:1 = MPE × 10, and at 4:1 = MPE × 4. Example: the VDS-15AX is rated ±0.02 mm, so it suits part tolerances of about ±0.2 mm at 10:1, or ±0.08 mm at 4:1.

2. Base length: what it can bridge

The base has to rest on solid surface on both sides of the opening, so the widest opening a gauge can span is always less than its base length. On our models the bases are 60 mm (NTD35-M), 63.5 mm (7211A, 7213A, DMS60), 100 mm (VDS 150–300 mm models, 7220A) and 101.6 mm (7212A, 7214A, DMS100, DMC100), and 250 mm on the 600 mm VDS models (product pages). Our reading: the 63.5 mm bases suit small faces and bosses where a long base would overhang, while the 100 mm-class bases bridge wider bores and pockets. AIMS Industrial adds that letting part of the base hang off the edge of the part introduces error, so choose a base that sits fully on the surface you measure from.

3. Coolant and dirt: IP67 or not

Only the VDS-P15, VDS-P20 and VDS-P30 are listed as coolant-proof IP67 in Mitutoyo's 571 series catalog. The VDS-15AX, 20AX and 30AX are standard ABS Digimatic models; an IP rating for them is Not confirmed, so choose the VDS-P models for coolant. The dial and vernier gauges have no electronics to protect, but AIMS Industrial notes that chips in a dial gauge's rack can make the dial skip, so they need to be kept clean.

4. Dial gauges: stroke and measuring force

The dial models split into two groups on their product pages: 7211A, 7212A and 7220A have a 10 mm stroke, ±0.015 mm and a measuring force of 1.4 N or less; 7213A and 7214A have a 30 mm stroke, ±0.030 mm and 2.5 N or less. The work consequence is arithmetic: a 30 mm stroke covers three times the depth change from one setting, at twice the rated error. All five list a measuring range of 0–200 or 0–210 mm; how the range beyond the stroke is reached (for example with interchangeable rods) is Not confirmed on our product pages.

5. Depth micrometers: rods and contact pressure

A depth micrometer's ratchet or friction stop applies the same force each time, which Machinist Guides recommends using when zeroing and measuring. The 0–25 mm DMS models have a single range. The digital DMC100-150MX and DMC100-300MX cover 0–150 and 0–300 mm with a 4 mm rod and a 0.001 mm display; their product pages list ±0.003 mm, but whether that figure covers every rod length is Not confirmed. For comparison, Insize states a separate rod accuracy that grows with length for its depth micrometers (Penn Tool listing). Machinist Guides advises checking a depth micrometer whenever the rod is changed, because dirt where the rod seats shifts the reading.

Mitutoyo depth gauges we stock, compared

Model (code) Type Range Display / graduation MPE Tightest tolerance at 10:1 / 4:1 (= MPE × 10 / × 4) Base Notes
VDS-15 (527-201) Vernier 0–150 mm 0.05 mm ±0.05 mm ±0.5 / ±0.2 mm 100 mm No battery
VDS-20 (527-202) Vernier 0–200 mm 0.05 mm ±0.05 mm ±0.5 / ±0.2 mm 100 mm No battery
VDS-30 (527-203) Vernier 0–300 mm 0.05 mm ±0.08 mm ±0.8 / ±0.32 mm 100 mm No battery
VDS-60 (527-204) Vernier 0–600 mm 0.05 mm ±0.10 mm ±1.0 / ±0.4 mm 250 mm No battery
7211A Dial 0–200 mm 0.01 mm ±0.015 mm ±0.15 / ±0.06 mm 63.5 mm 10 mm stroke, ≤1.4 N, rod ø10 mm
7212A Dial 0–200 mm 0.01 mm ±0.015 mm ±0.15 / ±0.06 mm 101.6 mm 10 mm stroke, ≤1.4 N
7220A Dial 0–200 mm 0.01 mm ±0.015 mm ±0.15 / ±0.06 mm 100 mm 10 mm stroke, ≤1.4 N
7213A Dial 0–210 mm 0.01 mm ±0.030 mm ±0.3 / ±0.12 mm 63.5 mm 30 mm stroke, ≤2.5 N
7214A Dial 0–210 mm 0.01 mm ±0.030 mm ±0.3 / ±0.12 mm 101.6 mm 30 mm stroke, ≤2.5 N
VDS-15AX (571-201-30) Digital 0–150 mm 0.01 mm ±0.02 mm ±0.2 / ±0.08 mm 100 mm Data output; IP rating Not confirmed
VDS-20AX (571-202-30) Digital 0–200 mm 0.01 mm ±0.02 mm ±0.2 / ±0.08 mm 100 mm Data output; IP rating Not confirmed
VDS-30AX (571-203-30) Digital 0–300 mm 0.01 mm ±0.03 mm ±0.3 / ±0.12 mm 100 mm Data output; IP rating Not confirmed
VDS-P15 (571-251-20) Digital 0–150 mm 0.01 mm ±0.02 mm ±0.2 / ±0.08 mm 100 mm Coolant-proof IP67, data output
VDS-P20 (571-252-20) Digital 0–200 mm 0.01 mm ±0.02 mm ±0.2 / ±0.08 mm 100 mm Coolant-proof IP67, data output
VDS-P30 (571-253-20) Digital 0–300 mm 0.01 mm ±0.03 mm ±0.3 / ±0.12 mm 100 mm Coolant-proof IP67, data output
VDS-60DC (571-205-10) Digital 0–600 mm 0.01 mm ±0.05 mm ±0.5 / ±0.2 mm 250 mm SR44 battery; IP rating Not confirmed
NTD35-M (571-100-20) Digital (tire) 0–25 mm 0.01 mm ±0.02 mm ±0.2 / ±0.08 mm 60 mm Data output
DMS60-25 (128-101) Depth micrometer 0–25 mm 0.01 mm ±0.003 mm ±0.03 / ±0.012 mm 63.5 mm Ratchet, clamp, rod ø4 mm
DMS60-25W (128-103) Depth micrometer 0–25 mm 0.01 mm ±0.003 mm ±0.03 / ±0.012 mm 63.5 mm Carbide measuring face, ratchet, clamp
DMS100-25 (128-102) Depth micrometer 0–25 mm 0.01 mm ±0.003 mm ±0.03 / ±0.012 mm 101.6 mm Ratchet, clamp, rod ø4 mm
DMS100-25W (128-104) Depth micrometer 0–25 mm 0.01 mm ±0.003 mm ±0.03 / ±0.012 mm 101.6 mm Carbide measuring face, ratchet, clamp
DMC100-150MX (329-250-30) Digital depth micrometer 0–150 mm 0.001 mm ±0.003 mm* ±0.03 / ±0.012 mm* 101.6 mm Data output, rod ø4 mm
DMC100-300MX (329-251-30) Digital depth micrometer 0–300 mm 0.001 mm ±0.003 mm* ±0.03 / ±0.012 mm* 101.6 mm Data output, rod ø4 mm

Range, display, MPE, base, stroke and force are Mitutoyo catalog data as shown on each linked product page; IP67 is given only where Mitutoyo's 571 series catalog lists it. The "tightest tolerance" column is our own arithmetic (MPE × 10 and MPE × 4) based on the 10:1 and 4:1 ratios described by MSC Industrial; it is a selection guide, not a Mitutoyo specification, and it ignores other error sources such as temperature and technique. *Whether ±0.003 mm applies across the full 0–150 / 0–300 mm range is Not confirmed. All 23 models are listed as made in Japan on their product pages.

MITUTOYO VDS-15 Depth gauge (527-201) 150mm Mitutoyo VDS-15 Depth Gauge, 150 mm (527-201) MITUTOYO VDS-20 Depth gauge (527-202) 200mm Mitutoyo VDS-20 Depth Gauge, 200 mm (527-202)

Which depth gauge for which job

Counterbores, pockets and blind holes in the machine shop

Mitutoyo VDS-P15 coolant-proof depth gauge

AIMS Industrial notes that counterbore depth tolerances are often ±0.1 mm or tighter on precision joints. At ±0.1 mm, a ±0.02 mm gauge does not meet 10:1 (that needs ±0.2 mm or looser) but does meet 4:1 (±0.08 mm), so a 150 mm digital gauge is a sensible default unless your drawing calls for 10:1. Next to a machine with coolant, choose the IP67 coolant-proof VDS-P15; on a dry bench the VDS-15AX.

View VDS-P15

O-ring grooves and seal seats

Mitutoyo DMS60-25 depth micrometer

AIMS Industrial points out that groove depth sets how much an O-ring is compressed, and gives 0.05 mm as an error that can matter on a critical groove. If your groove tolerance is, say, ±0.03 mm, that is below what a ±0.02 mm depth gauge covers at 4:1 (±0.08 mm), so it is depth micrometer work. The DMS60-25 (63.5 mm base) fits small housings; the DMS100-25 (101.6 mm base) bridges wider bores.

View DMS60-25

Logging depths to a PC or SPC

Mitutoyo DMC100-150MX digital depth micrometer

Every digital model in the table lists a data output terminal except the VDS-60DC, whose page does not say (product pages). For micrometer-level resolution with output, the DMC100-150MX shows 0.001 mm. Output models can connect to a PC through Mitutoyo USB input tools or U-WAVE (see our Mitutoyo data tools collection, and check the connecting cable for your model).

View DMC100-150MX

Tire tread depth (automotive)

Mitutoyo NTD35-M tire depth gauge

The NTD35-M is a digital tire depth gauge: 0–25 mm, 0.01 mm display, ±0.02 mm, 60 mm base and a data output terminal (product page). For a pass/fail check against a legal tread limit a simple gauge does the job; the NTD35-M makes sense when you record tread depth as data, for fleets or tire wear testing (our view).

View NTD35-M

Deep features and large parts

Mitutoyo VDS-60DC 600 mm digital depth gauge

For 300 mm, the VDS-30AX or coolant-proof VDS-P30 (±0.03 mm). For 600 mm, the digital VDS-60DC (±0.05 mm) or the vernier VDS-60 (±0.10 mm), both with a 250 mm base. AIMS Industrial notes that hand heat matters more on long gauges, so hold them by the base and let them settle to room temperature before critical readings.

View VDS-30AX

How to use a depth gauge

  1. Clean both surfaces. Wipe the base face and the part surface; a chip under the base adds its thickness to the reading (AIMS Industrial).
  2. Deburr the edge of the hole. A burr lifts the base and the gauge reads from the burr, not the surface (AIMS Industrial).
  3. Zero on a flat reference. Set the base on a surface plate and zero, using the ratchet on a depth micrometer (Machinist Guides).
  4. Hold the base down, then lower the rod. Keep one hand pressing the base flat and bring the rod down gently with the other; pushing hard on the rod flexes it (AIMS Industrial).
  5. Find the true bottom. If the rod lands on a corner radius it reads shallow; move the rod across the bottom to find the lowest point (AIMS Industrial). The same applies to the cone left by a drill point (our note).
  6. Blow out blind holes. Trapped cutting fluid or air can stop the rod short of the bottom; clear chips and fluid before measuring (AIMS Industrial).
  7. Repeat. Take two or three readings; if they do not agree, look for a burr, a tilted base or dirt before trusting any of them.

Why buy a Japanese-market Mitutoyo depth gauge? (facts we can confirm)

  • All 23 depth gauges and depth micrometers in the table are listed as made in Japan on their product pages.
  • Each product page states the maximum permissible error, so you can match a model to your tolerance with the arithmetic above instead of guessing from the display.
  • Mitutoyo order codes such as 571-201-30 are used worldwide; the model names (VDS-15AX) are Japanese catalog names, and inch versions sold in the US have different codes. Compare by code and specification.
  • We ship from Osaka and check each item in Japan before it goes out.

What we do not claim: that these gauges are more accurate than every other brand. Compare any two gauges on their stated maximum permissible error.

FAQ

Can I just use the depth rod on my caliper, or add a base to it?

This question comes up on machinist forums. In a Hobby-Machinist thread about a depth micrometer, one reply suggests a depth base that clamps onto a dial caliper as accurate enough for most work. AIMS Industrial's guide takes the other side for repeated or critical measurements: a caliper's narrow body does not stop you tilting it, while a depth gauge's wide base sits square on the part. Our view: a caliper (with or without a base) is fine for occasional checks with loose tolerances; once the tolerance is inside what the caliper's own error allows at 4:1, use a depth gauge or depth micrometer.

What is the difference between a depth gauge and a depth micrometer?

Both read from a base to a rod tip. On our models, the depth gauges are rated ±0.015 to ±0.10 mm and the depth micrometers ±0.003 mm (product pages). The mechanical DMS micrometers list a constant-pressure device (ratchet) so the contact force is the same each time; this is Not confirmed for the digital DMC models. The gauges cover longer ranges from one tool.

Does a 0.01 mm display mean the gauge is accurate to 0.01 mm?

No. The display (resolution) on the VDS-15AX is 0.01 mm; its maximum permissible error is ±0.02 mm (product page). Compare gauges on MPE.

How do I check a depth micrometer?

Machinist Guides describes zeroing it on a surface plate, then checking it with gauge blocks at several points in the range, and re-checking whenever the rod is changed.

Do these gauges read in inches?

The product pages for these Japanese-market models list metric (mm) specifications. Inch display is Not confirmed; ask us before ordering if you need it.

Related

Shipped directly from Japan

We ship genuine Mitutoyo instruments from Osaka with tracking (Japan Post, FedEx or DHL), and check each one before it leaves. For US orders, import duties are included in the price.

Browse Mitutoyo depth gauges

Sources

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