EN 1092-1 · Reverse search

Identify a flange: determine the size from measured dimensions

You have a flange in front of you, the marking is illegible or missing, and you need a replacement. Enter what you can measure – outside diameter, flange thickness, number of bolt holes, bolt circle. This page tells you the nominal sizes and pressure ratings to EN 1092-1 whose limit dimensions include your measured values, and for every dimension the table row it follows from.

The calculation does not use nominal dimensions but the limit dimensions of the standard. That is the difference from a table to look things up in: a manufactured flange practically never hits its nominal dimension, and the ranges of neighbouring sizes overlap. Anyone who only looks for the nearest nominal dimension gets an answer that looks more precise than it is.

No flange in front of you? The same reverse search exists for pipes, elbows, tees, reducers, caps and dished ends under Identify a component. This page remains the entry point for flanges – it only asks for flange dimensions and only calculates against EN 1092-1.

The four dimensions that count

The outside diameter takes two seconds to measure and narrows the choice down considerably at once. Measure the flange thickness from the sealing face to the back of the flange plate – a raised face is included and is not added. Count the number of bolt holes; it is the only characteristic without a tolerance and therefore separates sizes that are identical in all other dimensions. The bolt circle is taken from centre to centre of two opposite holes.

You do not have to enter all four. The fewer you enter, the more candidates remain – the page then tells you which dimension would decide.

Enter measured values

The reverse search calculates in the browser and needs JavaScript. Without JavaScript, the dimension tables will help you: Flange dimensions PN 6 to PN 40. Or send us the measured values – see below.

Why several sizes can match

Several candidates are a result, not an error. Two causes come together.

The tolerance bands overlap. At DN 50, a flange thickness specified as 18 mm may measure 19.0 mm, and one specified as 20 mm may measure 18.5 mm. Anyone who measures 18.7 mm has two candidates. Ranking by distance from the nominal dimension would be spurious precision – it would sort measuring errors, not distinguish sizes.

Some flanges are simply identical. From DN 10 to DN 40, PN 10, 16, 25 and 40 are dimensionally identical; from DN 50 to DN 150, PN 10 and PN 16 are identical. The search combines such sizes into one answer and names the pressure ratings side by side. Which one your part carries is shown in the marking.

Why the number of bolt holes is decisive

The number of bolt holes is not a dimension but a countable characteristic: it is 8 or 12, nothing in between. Consistently, the standard gives it no limit deviation. That is exactly why it separates where all other dimensions look the same: at DN 200, PN 10 and PN 16 hardly differ in outside diameter, but clearly in the number of bolt holes – eight against twelve. Counting the holes saves measuring again.

If no size matches

Then two things are possible, and both occur in practice.

The part follows a different standard. Existing plants contain withdrawn DIN standards, company standards and – particularly often in plants from project business – ASME B16.5. An inch flange looks confusingly similar to a metric one and still does not fit: EN 1092-1 and ASME B16.5 compared.

Or a dimension was measured differently from what the standard means. The classic case is the flange thickness: anyone who adds the raised face ends up systematically too high and finds nothing. The second most frequent case is the bolt circle, when it is taken across two neighbouring holes instead of two opposite ones.

If the part still remains unclear

This page calculates dimensions against the standard – nothing more. It says nothing about material, marking, surface finish or certificates, and no statement about the suitability of your component follows from its result.

If you need a statement about the whole part, we will take a look at it. We have been trading in piping material since 1922 and have had old parts from plants of every age on our desk: send us photos, measured values, the stamping and – if available – the inspection certificate. We determine product type, standard, DN, PN and material, name the approximate year of manufacture and tell you what replaces it today.

Frequently asked questions

Why do several sizes match my measured values?

Because the ranges the standard allows for neighbouring sizes overlap. A measured flange practically never hits the nominal dimension. Anyone who measures a flange thickness of 18.7 mm at DN 50 has two candidates – no calculation can remove that. Several candidates are therefore a result and not an error.

Why do some results show more than one pressure rating?

Because these flanges are dimensionally identical. From DN 10 to DN 40, PN 10, 16, 25 and 40 are identical; from DN 50 to DN 150, PN 10 and PN 16 are identical. Which pressure rating your part carries is then shown in the marking, not in the dimensions.

Which dimensions should I measure?

Outside diameter, flange thickness, number of bolt holes and bolt circle. Together, these four make every flange of pressure ratings PN 6 to PN 40 unambiguous. Outside diameter and number of bolt holes alone narrow the choice down considerably; the number of bolt holes separates pressure ratings that are identical in all other dimensions.

What does it mean if no size matches?

Two things are possible, and both occur: the part follows a different standard – for example ASME B16.5, a withdrawn DIN standard or a company standard. Or a dimension was measured differently from what the standard means. The most frequent case is the flange thickness: it is measured to the back of the plate, and a raised face is already included.