Product type
A digital caliper measures outside dimensions, inside dimensions, depth and step with one sliding instrument, and shows the result on a screen. It is the most used measuring tool in a machine shop and in an inspection bay, and its position is unrivalled for a quick check on a dimension that spans a range of sizes.
A digital caliper measures outside dimensions, inside dimensions, depth and step with one sliding instrument, and shows the result on a screen. It is the most used measuring tool in a machine shop and in an inspection bay, and its position is unrivalled for a quick check on a dimension that spans a range of sizes.
Its advantage is breadth rather than precision. One instrument covers a range of sizes and several measurement types, and it reads directly as a figure with no vernier scale to interpret. A micrometer measures a narrower range and one type of dimension, but to a finer resolution and at a controlled measuring force. The two are complementary, and reaching for a caliper on a job that calls for a micrometer is one of the commoner ways an out-of-tolerance part gets accepted.
The differences between calipers are not in the display but in the construction: the range, the resolution, the accuracy statement, whether the beam and jaws are hardened, whether the head is sealed against coolant, and whether a reading can be exported. This page covers what each of those decides, and where the instrument should give way to another.
The head carries a capacitive or inductive scale along the beam, and the electronics count its position relative to a zero point. Because the reading is a position along a beam, the accuracy statement is quoted over the full travel and is not uniform in effect: it is expressed as a tolerance across the range, so the uncertainty does not shrink when a small dimension is measured on a long instrument.
The measuring force is set by the operator’s thumb, which is the fundamental limitation. A caliper has no slip clutch and no constant-force mechanism, so the reading depends on how firmly the jaws are closed. On soft material or on a flexible part, the difference between a light and a firm touch can exceed the instrument’s own tolerance - and that is before any consideration of wear in the jaws.
On digital instruments the reference type is a practical distinction. An absolute type remembers its origin and is ready to read as soon as it is switched on; an incremental type has to be zeroed after switching on, and if it has been moved while off it will report a false value that looks entirely plausible. That difference matters most on a busy bench, where the tool is picked up and put down all day.
Most of the specification is fixed by these decisions rather than by the accuracy class. Each one constrains the next, which is why they are settled in order.
| Configuration | Options to fix | What it actually decides |
|---|---|---|
| Measuring range | Common shop sizes, up to long-reach instruments | Which parts can be measured at all, and whether a different instrument is needed for deep or large work. |
| Resolution | The last digit shown on the display | How finely the display reads. It is not the accuracy, and on most calipers the accuracy figure is the coarser of the two. |
| Accuracy statement | A tolerance quoted over the measuring range | Whether the instrument can support the tolerance being checked. On a small dimension measured on a long caliper, the range tolerance is what applies. |
| Jaws and beam construction | Hardened stainless, and whether the jaws are ground and lapped | How long the instrument holds its accuracy in daily use, and whether it tolerates abrasive or hardened parts without losing its edge. |
| Measurement functions | Outside, inside, depth and step measurement, and whether a lock screw is fitted | Whether one tool covers the whole inspection or several are needed, and whether a reading has to be held while it is recorded. |
| Zero setting | An absolute origin, or an incremental zero | Whether the tool can be picked up and read directly, or has to be zeroed first - which is where a plausible-looking wrong figure comes from. |
| Data output | None, or a data port for recording | Whether readings can be captured automatically, which matters where a batch record has to be produced. |
| Environmental sealing | Whether the head and scale are protected against coolant, water and dust | Whether the instrument survives the environment it is used in, which on a machine tool is the difference between months and years. |
| Factor | Why it decides the answer | How to settle it before enquiring |
|---|---|---|
| The dimension being measured | A caliper covers four measurement types, but not every geometry is reachable with standard jaws | State which dimension, and whether the jaws can physically reach the feature. |
| Size range | It sets the instrument, and a longer beam also carries a wider range tolerance | Give the smallest and largest dimension in the batch. |
| Tolerance to be checked | The accuracy statement has to be finer than the tolerance, with something in hand | Quote the drawing tolerance, not only the nominal size. |
| Resolution needed | Where the drawing calls for a figure the caliper cannot resolve reliably, the instrument is wrong for the job | State whether the tolerance needs a resolution the caliper cannot provide. |
| Surface and material of the part | Soft or flexible parts move under the jaws, and abrasive ones wear them | Describe the material, and whether it deforms under light pressure. |
| Environment of use | Coolant, swarf and dust decide whether sealing is needed | Describe the bench or machine the instrument will be used at. |
| Whether readings are recorded | A data output is only worth having if the data is captured | Say whether a batch record is produced, and in what form. |
If any of these are still open, send what is known. A quotation can be issued against a duty description and refined once the gaps are filled.
These are the types an enquiry for a digital caliper usually turns out to be, and the point at which the choice is genuinely decided.
| Nearest alternative | What separates it from a digital caliper |
|---|---|
| Vernier calipers | The same instrument with a graduated scale instead of electronics. It needs no battery, cannot be left switched on, and does not drift, which is why it is still used where a reading has to be dependable after long storage. Reading a vernier is slower and depends on the user’s eyesight. |
| Micrometers | Measure one type of dimension over a narrow range, with a finer resolution and a controlled measuring force. That force control is what makes it the more dependable instrument on a tolerance near its limit, and it is why a dimension that matters is measured with a micrometer and only checked with a caliper. |
| Depth gauges | Built for a slot, a bore shoulder or a recess, where a caliper depth rod often cannot reach squarely. On a deep or narrow feature the dedicated gauge gives a repeatable figure where the caliper rod tends to tilt. |
| Height gauges | Measure from a surface plate upwards, and can scribe or set a height in layout work. That turns a vertical dimension into a measurement from a reference plane, which a caliper cannot do at all. |
| Bore gauges | Measure an internal diameter at depth, with a self-centring action that finds the true diameter. The inside jaws of a caliper measure only at the surface, cannot reach into a bore, and do not centre themselves. |
| Gauge blocks | Not a measuring instrument but the reference against which these instruments are checked. A set of blocks of certified length is what establishes that a caliper is reading correctly, and a workshop that measures to a tolerance normally holds a set for that purpose. |
The boundary that matters most here is caliper against micrometer. Where a tolerance is close to what a caliper can hold, the reading has to come from an instrument whose measuring force does not depend on the operator.
The first reply can be a quotation rather than a set of questions if the enquiry carries these. Where a figure is not known, send the duty description and we will confirm what it implies.
Available products
Digital Calipers
Digital vernier caliper in 150, 200 and 300 mm ranges with a 0.01 mm display, metric and inch switching, zero at any position, and an IP54 version for wet or dusty work.
Also in Dimensional Measurement
Every type we quote for under Dimensional Measurement. A type with no link yet is still quoted for - it is described on the Dimensional Measurement overview, and gets a page of its own as soon as a model is published against it.
Frequently asked
The instrument has to be finer than the tolerance, with something in hand. A micrometer measures one dimension over a narrow range at a controlled force; a caliper measures several dimensions over a wide range at whatever force the operator applies. Where a tolerance sits close to what a caliper can hold, the reading belongs on a micrometer, with the caliper used for the checks that are not near a limit.
Usually because of measuring force and contact geometry. A caliper is closed by hand and touches the part along a line, so a soft or slightly oval part reads differently under a light and a firm touch. A micrometer has a friction or ratchet stop that fixes the force, and it contacts the surface over a defined face. On a part with any of those characteristics the difference is real rather than an error in either instrument.
No. The resolution is what the last digit can show; the accuracy statement is a tolerance over the measuring range. On most calipers the accuracy tolerance is the coarser of the two, so a display showing hundredths does not mean the reading is dependable to hundredths. Both figures appear in the specification, and they should be read together.
Where it is used near coolant, swarf or a washdown, yes. An unprotected head draws in fine debris and mist, and the scale begins to miss counts or stick - which shows up as an intermittent wrong reading rather than as an obvious failure. In a dry inspection room the sealing buys nothing, and the simpler instrument is the better choice.
Send the specification and we will confirm the matching model, availability and lead time. Minimum order quantity is 1 pc.
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