Runout vs total runout: what each GD&T control actually catches

By Rajadurai R — Founder, CadNexa · 14 years plant-head experience

A hydraulic cylinder rod passes every diameter check on the final inspection report. Roundness is fine. Straightness is fine. Then it goes into the customer's assembly and wobbles at 1,400 rpm like a bent bicycle wheel. I have seen this exact scenario twice in 14 years of running plants — and both times the root cause was the same: the drawing needed a runout control, and nobody had checked it as one.

Runout is the GD&T control that catches wobble. It comes in two strengths — circular runout (one arrow) and total runout (two arrows) — and mixing them up costs real money, because total runout is significantly more expensive to hold and to measure. This guide explains what each one controls, how to measure both, and which to put on the drawing.

What runout actually controls

Runout is a composite control. When a surface spins about a datum axis, a dial indicator held against it moves for two separate reasons: the surface is not perfectly round (a form error), and the surface is not perfectly centred on the axis (a location error). Runout does not separate the two — it limits their combined effect, which is exactly what a rotating assembly feels in service.

That is why runout always requires a datum axis. The feature control frame must reference a datum (often two, like A–B for a shaft held between two bearing journals), and the tolerance value is the maximum permitted Full Indicator Movement (FIM) — the total swing of the needle, not a ± value. A runout of 0.05 mm means the needle may move at most 0.05 mm from its lowest to its highest reading. If you are new to reading these callouts, start with our feature control frame guide and the datum reference frame explainer.

Circular runout: one arrow, one circle at a time

Circular runout (single arrow symbol) is checked one cross-section at a time. You rotate the part 360° about the datum axis with the indicator held at a fixed axial position, and record the FIM. Then you may move the indicator to another cross-section and repeat — but each section is evaluated independently.

• Tolerance zone: two concentric circles (2D), per section
• Catches: out-of-roundness and eccentricity at each section
• Does not catch: taper, barrel shape or bow along the length — each section can pass individually while the axis drifts
• Applied to: cylindrical surfaces, and also faces and cones (measured normal to the surface)

Example callout on a pump shaft: circular runout 0.03 to A–B on a ⌀25 h6 seal journal. Every circular element of that journal must show ≤0.03 mm FIM when the shaft rotates on its two bearing datums.

Total runout: two arrows, the entire surface at once

Total runout (double arrow symbol) is checked over the whole surface simultaneously. The part rotates about the datum axis while the indicator traverses axially along the surface, and every reading taken anywhere on that sweep counts toward one single FIM value.

• Tolerance zone: two coaxial cylinders (3D), covering the full feature length
• Catches: everything circular runout catches, plus taper, barrel/hourglass form, bow and axial straightness error
• Applied to: cylindrical surfaces and flat faces perpendicular to the datum axis (where it also controls flatness of the face)

Because one FIM budget covers the whole surface, a part that passes circular runout at every individual section can still fail total runout — a tapered journal is the classic case. Each circle is round and centred, but the diameters shrink along the length, so the axial sweep picks up the change.

Circular vs total runout: side by side

How to measure runout

With a dial indicator on the bench

1. Establish the datum axis physically. Hold the part between centres if centre holes exist, or support the datum journals on V-blocks, or grip the datum diameter in a high-accuracy chuck or collet.
2. Zero the indicator against the controlled surface, perpendicular to it.
3. Rotate the part 360° and record the FIM. For circular runout, repeat at several sections and report the worst section. For total runout, traverse the indicator smoothly along the surface during rotation and report one overall FIM.

One warning from the shop floor: V-blocks introduce error when the datum journal itself has lobing — a three-lobed journal sitting in a 90° V-block can show runout readings up to 2× the true value, or hide error entirely, depending on lobe orientation. Between-centres setups avoid this, which is why precision shafts carry centre holes.

On a CMM

A CMM constructs the datum axis from measured cylinders, scans circular elements (or the full surface for total runout), and evaluates FIM mathematically. This removes fixturing error but adds programming time — plan the datum strategy before probing, as covered in our CMM inspection planning guide. For high-volume checking, a dedicated runout fixture with a dial indicator remains faster and cheaper than CMM time.

Which one should you specify?

• Circular runout when the function is sealing or moderate-speed rotation: lip-seal journals, pulley diameters, sprocket seats. It is cheaper to make and to check.
• Total runout when the whole surface mates or runs at speed: bearing seats, gear bores, machine-tool spindle noses, brake rotor friction faces. Anywhere taper or bow would cause vibration, edge loading or premature bearing failure.

A useful rule from ASME Y14.5-2018 practice: specify the cheapest control that protects the function. Do not put total runout on every diameter of a shaft "to be safe" — you will pay for grinding you do not need.

Common mistakes

• Reading the tolerance as ±. Runout 0.05 is a total FIM of 0.05 mm, not ±0.05. Inspectors who double it pass bad parts.
• Using runout in place of position. Runout only works for surfaces of revolution about a datum axis. A bolt-hole pattern needs position, not runout.
• Still specifying concentricity. ASME Y14.5-2018 removed the concentricity symbol; runout or position is the modern replacement. If a legacy drawing shows concentricity, agree the verification method with the customer before quoting.
• No datum in the frame. A runout callout without a datum reference is not verifiable. Reject or query the drawing.
• Checking total runout at fixed sections only. Without the axial traverse you are measuring circular runout and calling it total — a common audit finding in FAI reviews.

How CadNexa helps

On a shaft drawing with 15 runout and diameter callouts, every one needs a balloon number and a row in the inspection report. The CadNexa auto-balloon tool — Smart Detect plus Box+Balloon OCR — picks up feature control frames, including runout symbols and their datum references, straight off the PDF and builds the characteristic list for the AS9102 or PPAP report. What takes an afternoon with a highlighter takes minutes in the browser, and the CSV export drops directly into your CMM or inspection planning sheet.

Frequently asked questions

Is runout the same as concentricity?

No. Concentricity (now removed from ASME Y14.5-2018) controlled the location of median points only and was notoriously hard to measure. Runout is a composite of coaxiality and form measured as a simple indicator reading, which is why it replaced concentricity in most applications.

Can runout be specified without a datum?

No. Runout is meaningless without a datum axis — the part has to rotate about something. Every runout feature control frame must reference at least one datum, commonly a pair like A–B for shafts supported at two journals.

Is total runout always tighter than circular runout?

For the same tolerance value, total runout is always the more demanding control because one FIM budget covers the entire surface, including taper and bow. A part meeting total runout 0.05 automatically meets circular runout 0.05, never the reverse.

Does runout control diameter size?

No. Size is controlled by the diameter tolerance independently. A journal can be at perfect size and still fail runout, or hold zero runout while being out of size. Both must be checked and reported separately in the FAI.

For more practical GD&T and inspection guides, browse the CadNexa learning centre.