{"id":702,"date":"2026-04-03T21:21:05","date_gmt":"2026-04-03T15:51:05","guid":{"rendered":"https:\/\/www.xtd-ss.com\/blog\/?p=702"},"modified":"2026-04-03T21:21:07","modified_gmt":"2026-04-03T15:51:07","slug":"stainless-steel-pipe-size-chart-nps-schedule-od","status":"publish","type":"post","link":"https:\/\/www.xtd-ss.com\/blog\/stainless-steel-pipe-size-chart-nps-schedule-od\/","title":{"rendered":"SS Pipe Sizing Guide: NPS, Schedule &amp; OD Explained"},"content":{"rendered":"<div id=\"bsf_rt_marker\"><\/div>\n<p class=\"wp-block-paragraph\">Ordering <a href=\"https:\/\/www.xtd-ss.com\/stainless-steel-pipe.html\">stainless steel pipe<\/a> without understanding NPS, schedule, and OD leads to wrong sizes, wasted material, and project delays. These 3 dimensions define every pipe you buy, but they confuse even experienced engineers.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This guide explains how NPS, schedule, and OD work together. We cover the sizing system, common size-to-OD conversions, schedule-to-wall-thickness data, and a practical method for selecting the right pipe size for your project.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Is NPS (Nominal Pipe Size)?<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img fetchpriority=\"high\" decoding=\"async\" width=\"1024\" height=\"572\" src=\"https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/nps-1024x572.png\" alt=\"Diagram showing various NPS sizes compared\" class=\"wp-image-1165\" srcset=\"https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/nps-1024x572.png 1024w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/nps-300x167.png 300w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/nps-768x429.png 768w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/nps.png 1376w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">NPS stands for <strong>Nominal Pipe Size<\/strong>. It is a North American designation that identifies a pipe by a number, like NPS 2, NPS 4, or NPS 10. However, the NPS number does not correspond to the actual pipe OD: the NPS number does not equal the actual OD or ID of the pipe.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For pipe sizes NPS 1\/8 through NPS 12, the NPS number is a label,&nbsp; not a measurement. For example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NPS 2 pipe has an actual OD of 60.3 mm (2.375 inches) \u2014 not 2 inches<\/li>\n\n\n\n<li>NPS 4 pipe has an actual OD of 114.3 mm (4.500 inches) \u2014 not 4 inches<\/li>\n\n\n\n<li>NPS 6 pipe has an actual OD of 168.3 mm (6.625 inches) \u2014 not 6 inches<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">For pipe sizes NPS 14 and above, the NPS number equals the OD in inches. NPS 14 pipe has an OD of exactly 355.6 mm (14.000 inches).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The international equivalent of NPS is DN (Diam\u00e8tre Nominal). DN is expressed in millimetres; DN 50 corresponds to NPS 2, DN 100 to NPS 4, and so on.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Is a Pipe Schedule?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Pipe schedule is a wall thickness designation. It indicates how thick the pipe wall is for a specific NPS size. Higher schedule numbers indicate thicker walls.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Common schedule numbers for stainless steel pipe include:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>5S and 10S \u2014 thin wall (the \u201cS\u201d stands for stainless steel series)<\/li>\n\n\n\n<li>40S \u2014 standard wall<\/li>\n\n\n\n<li>80S \u2014 extra strong<\/li>\n\n\n\n<li>120, 160 \u2014 heavy wall<\/li>\n\n\n\n<li>XXS \u2014 double extra strong (the thickest standard wall)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The schedule number originally came from a formula: Schedule = (1,000 \u00d7 P) \/ S, where P is the internal pressure in psi, and S is the allowable stress in psi. Today, schedule numbers are standardised values in <a href=\"https:\/\/en.wikipedia.org\/wiki\/Nominal_Pipe_Size\" target=\"_blank\" rel=\"noopener\">ASME B36.19M<\/a> (for stainless steel) and ASME B36.10M (for carbon steel).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">One critical point: the same schedule number gives different wall thicknesses at different NPS sizes. Schedule 40S for NPS 2 is 3.91 mm, but Schedule 40S for NPS 8 is 8.18 mm.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What Is OD (Outside Diameter)?<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" width=\"1024\" height=\"683\" src=\"https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/outside-diameter-1024x683.png\" alt=\"\" class=\"wp-image-1164\" srcset=\"https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/outside-diameter-1024x683.png 1024w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/outside-diameter-300x200.png 300w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/outside-diameter-768x512.png 768w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/04\/outside-diameter.png 1536w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">OD is the actual outside diameter of the pipe measured in millimetres or inches. In contrast to NPS, the OD is a real physical measurement that can be validated using a calliper.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Every NPS size has a fixed OD that does not change regardless of the schedule. When you increase the schedule, only the wall thickness increases inward; the OD stays the same.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This means:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NPS 4 Schedule 5S has an OD of 114.3 mm<\/li>\n\n\n\n<li>NPS 4 Schedule 80S also has an OD of 114.3 mm<\/li>\n\n\n\n<li>The difference is wall thickness: 1.65 mm (5S) versus 8.56 mm (80S)<\/li>\n\n\n\n<li>The ID (inside diameter) changes with schedule: ID = OD &#8211; (2 \u00d7 wall thickness).<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">NPS to OD Conversion Table<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This table converts the 20 most common NPS sizes to their actual OD in both millimetres and inches. Use this for ordering and design.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>NPS<\/strong><\/td><td><strong>DN<\/strong><\/td><td><strong>OD (mm)<\/strong><\/td><td><strong>OD (inches)<\/strong><\/td><\/tr><tr><td>1\/8<\/td><td>6<\/td><td>10.3<\/td><td>0.405<\/td><\/tr><tr><td>1\/4<\/td><td>8<\/td><td>13.7<\/td><td>0.540<\/td><\/tr><tr><td>3\/8<\/td><td>10<\/td><td>17.1<\/td><td>0.675<\/td><\/tr><tr><td>1\/2<\/td><td>15<\/td><td>21.3<\/td><td>0.840<\/td><\/tr><tr><td>3\/4<\/td><td>20<\/td><td>26.7<\/td><td>1.050<\/td><\/tr><tr><td>1<\/td><td>25<\/td><td>33.4<\/td><td>1.315<\/td><\/tr><tr><td>1-1\/4<\/td><td>32<\/td><td>42.2<\/td><td>1.660<\/td><\/tr><tr><td>1-1\/2<\/td><td>40<\/td><td>48.3<\/td><td>1.900<\/td><\/tr><tr><td>2<\/td><td>50<\/td><td>60.3<\/td><td>2.375<\/td><\/tr><tr><td>2-1\/2<\/td><td>65<\/td><td>73.0<\/td><td>2.875<\/td><\/tr><tr><td>3<\/td><td>80<\/td><td>88.9<\/td><td>3.500<\/td><\/tr><tr><td>4<\/td><td>100<\/td><td>114.3<\/td><td>4.500<\/td><\/tr><tr><td>5<\/td><td>125<\/td><td>141.3<\/td><td>5.563<\/td><\/tr><tr><td>6<\/td><td>150<\/td><td>168.3<\/td><td>6.625<\/td><\/tr><tr><td>8<\/td><td>200<\/td><td>219.1<\/td><td>8.625<\/td><\/tr><tr><td>10<\/td><td>250<\/td><td>273.1<\/td><td>10.750<\/td><\/tr><tr><td>12<\/td><td>300<\/td><td>323.9<\/td><td>12.750<\/td><\/tr><tr><td>14<\/td><td>350<\/td><td>355.6<\/td><td>14.000<\/td><\/tr><tr><td>16<\/td><td>400<\/td><td>406.4<\/td><td>16.000<\/td><\/tr><tr><td>20<\/td><td>500<\/td><td>508.0<\/td><td>20.000<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">For a complete reference including all sizes and schedules, see our <a href=\"https:\/\/www.xtd-ss.com\/pipe-size-chart.html\">pipe size chart<\/a>.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Schedule to Wall Thickness Table<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This table shows wall thickness in mm for 6 common NPS sizes across 5 schedule designations. All values follow ASME B36.19M for stainless steel pipe.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>NPS<\/strong><\/td><td><strong>Sch 5S (mm)<\/strong><\/td><td><strong>Sch 10S (mm)<\/strong><\/td><td><strong>Sch 40S (mm)<\/strong><\/td><td><strong>Sch 80S (mm)<\/strong><\/td><td><strong>Sch 160 (mm)<\/strong><\/td><\/tr><tr><td><strong>1<\/strong><\/td><td>1.24<\/td><td>1.73<\/td><td>3.38<\/td><td>4.55<\/td><td>\u2014<\/td><\/tr><tr><td><strong>2<\/strong><\/td><td>1.65<\/td><td>2.77<\/td><td>3.91<\/td><td>5.54<\/td><td>8.74<\/td><\/tr><tr><td><strong>3<\/strong><\/td><td>1.65<\/td><td>3.05<\/td><td>5.49<\/td><td>7.62<\/td><td>11.13<\/td><\/tr><tr><td><strong>4<\/strong><\/td><td>1.65<\/td><td>3.05<\/td><td>6.02<\/td><td>8.56<\/td><td>13.49<\/td><\/tr><tr><td><strong>6<\/strong><\/td><td>1.65<\/td><td>3.40<\/td><td>7.11<\/td><td>10.97<\/td><td>18.26<\/td><\/tr><tr><td><strong>8<\/strong><\/td><td>1.65<\/td><td>3.76<\/td><td>8.18<\/td><td>12.70<\/td><td>20.62<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Notice how Schedule 5S stays at 1.65 mm for NPS 2 through NPS 8. That same thin wall carries very different pressure ratings depending on the OD. An NPS 2 Sch 5S pipe withstands higher pressure than an NPS 8 Sch 5S pipe due to its smaller outer diameter-to-wall thickness ratio.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How NPS, Schedule, and OD Work Together<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Here is the relationship in simple terms:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>NPS determines the OD (as per ASME B36.19M).<\/li>\n\n\n\n<li>The schedule determines the wall thickness (which varies by NPS).<\/li>\n<\/ol>\n\n\n\n<ol start=\"3\" class=\"wp-block-list\">\n<li>ID = OD minus (2 \u00d7 wall thickness)<\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">When you order a pipe, you specify 3 things:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NPS (or OD in mm)<\/li>\n\n\n\n<li>Schedule (or wall thickness in mm)<\/li>\n\n\n\n<li>Material grade (e.g., TP316L per <a href=\"https:\/\/www.xtd-ss.com\/astm-a312-pipes.html\">ASTM A312<\/a>)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">That gives the manufacturer everything needed to produce your pipe.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">How to Select the Right Pipe Size: 4 Steps<\/h2>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" width=\"1024\" height=\"843\" src=\"https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/03\/steps-to-select-right-pipe-size-visual-selection-1024x843.jpeg\" alt=\"\" class=\"wp-image-750\" srcset=\"https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/03\/steps-to-select-right-pipe-size-visual-selection-1024x843.jpeg 1024w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/03\/steps-to-select-right-pipe-size-visual-selection-300x247.jpeg 300w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/03\/steps-to-select-right-pipe-size-visual-selection-768x632.jpeg 768w, https:\/\/www.xtd-ss.com\/blog\/wp-content\/uploads\/2026\/03\/steps-to-select-right-pipe-size-visual-selection.jpeg 1500w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Step 1: Determine the Flow Rate<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Determine how much fluid your system needs to transport per hour (m\u00b3\/h or GPM). This determines the minimum interior area of the pipe.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Step 2: Calculate the Required ID<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Use the flow rate and the recommended flow velocity for your fluid. For example:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Liquid service: 1.5\u20133.0 m\/s (5\u201310 ft\/s) typical<\/li>\n\n\n\n<li>Gas service: 15\u201330 m\/s (50\u2013100 ft\/s) typical<\/li>\n\n\n\n<li>Steam service: 25\u201350 m\/s (80\u2013160 ft\/s) typical<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The formula is: ID = \u221a(4 \u00d7 Q \/ (\u03c0 \u00d7 V)), where Q = flow rate in m\u00b3\/s and V = velocity in m\/s.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Step 3: Select the NPS<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Find the NPS size whose ID at your chosen schedule matches or surpasses the calculated ID. You may need to check several schedules.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Step 4: Verify the Pressure Rating<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Calculate the specified working pressure per ASME B31.3 to confirm that the chosen NPS and schedule can withstand your design pressure at the operating temperature.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If the pressure check fails, increase the schedule number and recheck.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Common Mistakes in Pipe Sizing<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Avoid these 4 common errors:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Assuming NPS equals OD, NPS 2 is not a 2-inch OD. Check the conversion table above.<\/li>\n<\/ol>\n\n\n\n<ol start=\"2\" class=\"wp-block-list\">\n<li>Using carbon steel schedule tables for stainless steel, Stainless steel uses ASME B36.19M schedules (5S, 10S, 40S, 80S). Carbon steel uses B36.10M (STD, XS, XXS). The wall thicknesses can differ.<\/li>\n<\/ol>\n\n\n\n<ol start=\"3\" class=\"wp-block-list\">\n<li>Ignoring corrosion allowance, add 1.0\u20133.0 mm to the calculated minimum wall for expected corrosion over the design life.<\/li>\n<\/ol>\n\n\n\n<ol start=\"4\" class=\"wp-block-list\">\n<li>Specifying Schedule 40 by default, not every application needs Schedule 40. For low-pressure utility service, Schedule 10S saves weight and cost. For high-pressure service, you may need Schedule 80 or above.<\/li>\n<\/ol>\n\n\n\n<h2 class=\"wp-block-heading\">DN vs NPS: What Is the Difference?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The terms DN (Diam\u00e8tre Nominal) and NPS (Nominal Pipe Size) denote the same pipe sizes but are numbered differently:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>NPS uses inches (NPS 2, NPS 4, NPS 6)<\/li>\n\n\n\n<li>DN uses millimetres (DN 50, DN 100, DN 150)<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">They map to the same physical OD. DN 50 = NPS 2 = 60.3 mm OD. DN 100 = NPS 4 = 114.3 mm OD.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">European and Asian projects typically use DN. North American projects use NPS. Both systems are defined in ASME B36.19M and follow the same dimensional tables.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Stainless Steel Pipe Sizing for Our Products<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">We manufacture <a href=\"https:\/\/www.xtd-ss.com\/stainless-steel-seamless-pipe.html\">stainless steel seamless pipes<\/a> from NPS 1\/8 (6 mm OD) to NPS 24 (610 mm OD) in schedules from 5S to XXS. Our wall thickness range goes up to 60 mm for heavy wall applications.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Available grades include 304, 304L, 316, 316L, 321, 347, duplex 2205, super duplex 2507, and nickel alloys. All pipes follow ASTM A312, A790, or the applicable ASTM B-series standard.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Visit our <a href=\"https:\/\/www.xtd-ss.com\/pipe-size-chart.html\">pipe size chart<\/a> for the full dimensional reference.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">NPS identifies the pipe size, schedule sets the wall thickness, and OD is the actual measured outside diameter. These 3 values define every stainless steel pipe order. Use the NPS-to-OD table and the schedule-to-wall table in this guide to get your dimensions right.<br>Start with flow rate, calculate the ID, pick the NPS, and verify the pressure rating. When in doubt, <a href=\"https:\/\/www.xtd-ss.com\/contact-us.html\">contact us<\/a>. We help customers select the right pipe size, grade, and schedule every day.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Ordering stainless steel pipe without understanding NPS, schedule, and OD leads to wrong sizes, wasted material, and project delays. These 3 dimensions define every pipe you buy, but they confuse even experienced engineers. This guide explains how NPS, schedule, and OD work together. We cover the sizing system, common size-to-OD conversions, schedule-to-wall-thickness data, and a [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":1113,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[38,39,40,37],"class_list":["post-702","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-pipe-knowledge","tag-nominal-pipe-size","tag-nps","tag-pipe-schedule","tag-pipe-size-chart"],"_links":{"self":[{"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/posts\/702","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/comments?post=702"}],"version-history":[{"count":7,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/posts\/702\/revisions"}],"predecessor-version":[{"id":1166,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/posts\/702\/revisions\/1166"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/media\/1113"}],"wp:attachment":[{"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/media?parent=702"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/categories?post=702"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xtd-ss.com\/blog\/wp-json\/wp\/v2\/tags?post=702"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}