Weld Inches — Companion Article

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title: Weld inches tool_name: Weld Inches tool_version: 1.0.0 tool_url: /tools-training/weld-inch/ status: DRAFT – pending owner engineering review last_verified: 2026-10-11 companion_url: /companion-weld-inch/ how_this_calculation_works: /companion-weld-inch/ —

What this tool does

Weld Inches estimates shop weld inches from joints you list, and it estimates how a straight pipe run splits into spools. Weld inches are the nominal size multiplied by the number of welds. A slip-on flange counts as two welds. Every other joint on the page counts as one.

The spool count is the pipe run divided by the maximum spool length, rounded up. Field welds are one fewer than the number of spools. That count is shown apart from the shop weld inches.

When to use it

Use it when you want a first fabrication estimate: how many diameter-inches are in a list of joints, and how many field welds a straight run would need if each spool is limited to a length you choose. The usual starting length on the page is 6 m.

Use it before a weld map exists. Once the isometric is split, the spool drawing is the quantity. This page does not replace that drawing.

Inputs

Each joint row takes three entries:

• Nominal size, as an NPS number. NPS 6 is 6. NPS 1/2 is 0.5. NPS 2-1/2 is 2.5.
• Joint type: butt weld, socket weld, branch / olet, stub-in, slip-on flange, or weld-neck flange.
• Quantity, a whole number of those joints.

Rows can be added and removed. The shop total updates as you type.

The schedule factor is off until you turn it on. With it on, each row needs a schedule, and you type one factor for that schedule. The same schedule text shares one factor. The factor is user-defined. It is not a standard, and the page does not assign one to heavy wall.

The spool estimate takes:

• Units, metres or feet.
• Total pipe run.
• Maximum spool length. It starts at 6 m. In feet that same length is shown as 19.685 ft.
• Field-weld allowance, optional. Extra field welds, as a whole number. Blank means none.

How it works

Shop weld inches for a row are the nominal size, times the quantity, times the welds in that joint. A slip-on flange contributes two welds. A butt weld, a socket weld, a branch or olet, a stub-in, and a weld-neck flange each contribute one.

The shop total adds those rows. The breakdown repeats the same inches by joint type.

If the schedule factor is on, each row’s weld inches are multiplied by the factor you typed for its schedule. The unweighted inches stay visible. Turning the factor off leaves the inches unweighted, even if a number is still stored for a schedule.

Spools are the pipe run divided by the maximum spool length, rounded up. A run of 20 m with a maximum of 6 m is 4 spools, because 20 ÷ 6 is more than 3 and not more than 4. The lengths are 6 m, 6 m, 6 m, and a remainder of 2 m. An even split, such as 18 m at 6 m, is 3 spools of 6 m and has no short remainder.

Field welds from the split are the spool count minus 1. A single spool has no field weld. The allowance, if you type one, is added to that count. It is not given a position on the run.

Metres and feet use 0.3048 m per foot. The spool count is taken from the lengths on screen, so 20 m at 6 m and 65.617 ft at 19.685 ft are the same split.

Understanding the result

The results card has two parts, and they are not one number.

Shop weld inches are the diameter-inches of the joints you listed. The card shows each row and the total by joint type. With the factor on, it also shows the weighted inches and says the factor is user-defined.

Field welds are a count of joints between spools. The card states that this count is not added to the shop weld inches. It lists the spool lengths, the field welds from the split, and the field welds including the allowance.

The sketch is the same split, drawn to scale along the run. A 6 m spool is three times the drawn length of a 2 m spool. Each spool is dimensioned, including the short last spool. When that label does not fit between the arrows, it sits beside the short dimension. The whole run is dimensioned. A field weld is a double line across the pipe and a small flag marked FW. The allowance is not drawn. The width of the pipe on the sketch is not an outside diameter.

Export CSV writes those totals: the shop joints, the shop total, the run, the maximum spool length, the spool lengths, the spool count, and the field-weld counts.

Engineering considerations

Diameter-inches are a shop planning measure. They are not a weld volume, a man-hour figure, or a length of weld metal. A 6-inch butt weld is 6 weld inches on this page because the nominal size is 6, not because the outside diameter is 6.

A slip-on flange is two fillet welds on this page, one each side. A weld-neck flange is one butt weld. A branch, an olet, and a stub-in are each counted as one weld at the branch nominal size you type. The page does not compute a branch circumference from an outside diameter.

The spool split is a length split only. It does not stop at a fitting, a branch, a change of direction, a shipping frame, or a galvanising bath. The last spool is whatever length remains. Field welds from that split are not sized, so they stay a count unless you also list those joints in the shop rows. Listing them in both places would count them twice. The page does not do that for you.

The schedule factor is for a heavy-wall allowance you choose to apply. Two rows labelled with the same schedule text receive the same factor. The page will multiply by 1.5 if you type 1.5. That 1.5 is not a code factor.

Example

Shop joints, with the schedule factor off:

Joint	NPS	Quantity	Welds	Weld inches
Butt weld	6	8	8	48
Socket weld	4	6	6	24
Branch / olet	2	4	4	8
Stub-in	2	2	2	4
Slip-on flange	6	2	4	24
Weld-neck flange	8	2	2	16
Shop total			26	124

The two slip-on flanges are 4 welds because each flange counts as 2.

Spool estimate: pipe run 20 m, maximum spool length 6 m. Spools = 4. Lengths 6 m, 6 m, 6 m, and 2 m. Field welds from the split = 3. Allowance blank, so field welds including allowance = 3. Those 3 are not included in the 124.

The same run in feet is 65.617 ft with a maximum of 19.685 ft, and the split is still 4 spools and 3 field welds.

With the schedule factor on, one NPS 10 butt weld and a factor of 1.5 for schedule 160 is 10 weld inches and 15 weighted weld inches. The 1.5 is a number you type. It is not a standard.

Standards and references

This page does not store a standards table and it does not read a licensed or interim standard. Weld inches, the slip-on count of 2, and the spool split are the method written on the page. There is no ASME, API, or company factor behind the schedule weight. No provenance note is shown, because the page is not drawing values from an unlicensed standard.

Limitations and disclaimer

This is an estimate. It is not a fabrication quantity, a weld map, a cut list, or a material take-off. It needs a review before anyone uses it to order work.

It does not place welds on an isometric. It does not know which joints are already field welds. It does not split the run at fittings or changes of direction. It does not check a shipping limit other than the length you type. The sketch draws at most 40 spools; the count above that is still reported and is not drawn. Nominal size is not an outside diameter. The field-weld allowance is extra joints you type, not a code allowance.

Use the tool

Calculate now: Weld Inches

Related tools

• Cut Length is the pipe cut between two fittings. It does not count welds.
• Pipe volume is the internal volume of a run. It does not split spools.
• Line BOM lists catalogue items and quantities. It does not calculate weld inches.