Mississippi Residential Plumbing

Mississippi Residential Plumbing Exam: What You Need to Know to Pass in 2026

You've put in the work on job sites. Now you need to prove it on paper. The Mississippi Residential Plumbing exam stands between you and your license — and knowing exactly what's on it makes all the difference. This guide breaks down the exam format, the topics that carry the most weight, what to study, and what to bring on test day. Start by taking our free practice exam to see where you stand right now.

Mississippi Residential Plumbing Exam Overview

The exam is administered by PSI on behalf of the state licensing website. Here's what you're looking at:

• Questions: 80 scored questions
• Time: 240 minutes (4 hours)
• Passing score: 70% — that's 56 out of 80 questions correct
• Format: Computer-based, open book
• Location: PSI testing centers across Mississippi

The exam is open book, which sounds like a relief — and it is, if you're prepared. The catch is that you only have 3 minutes per question on average. Slow page-flipping will kill your time. Speed and familiarity with your references matter as much as knowing the material.

Scores appear on your screen the moment you finish. Pass, and you get a successful notification plus a performance summary. Don't pass, and you get a diagnostic report showing your strengths and weaknesses by topic — useful information for your next attempt.

Topics Covered on the Mississippi Residential Plumbing Exam

Here's how the 80 scored questions break down by topic. Study time should track these weights — not what's easiest, but what's tested most.

• Drain, Waste and Vent and Sewers (17 questions) — The heaviest topic on the exam. DFU values, drain sizing, slope requirements, cleanout placement, and DWV pipe materials. Know this cold.
• General Plumbing Knowledge and Regulations (15 questions) — Permits, inspections, code enforcement, stop work orders, and terminology. Straightforward code-reading questions.
• Isometric Analysis (9 questions) — Reading riser diagrams, assigning DFU values, and sizing drains and stacks from a diagram. Expect to do actual load calculations here.
• Piping, Valves, and Controls (6 questions) — Pipe materials, joint methods, backflow prevention, and water supply system design.
• Specialty Applications (6 questions) — Graywater systems, rainwater collection, solar thermal systems, and nonpotable water reuse.
• Fuel Gas (5 questions) — Gas piping materials, sizing methods, pressure testing, and combustion air requirements.
• Piping (5 questions) — Water supply and drainage piping standards, pipe sizing, and separation requirements.
• Fixtures and Equipment (4 questions) — Fixture minimums by occupancy, installation clearances, water heater safety devices.
• Water Supply (4 questions) — Backflow prevention, pressure requirements, and distribution design.
• Safety (4 questions) — PPE, excavation cave-in protection, confined space entry, and fire extinguisher requirements.
• LP Gas (3 questions) — Propane pipe sizing, two-stage regulator systems, and allowable operating pressures.
• Fuel Oil (2 questions) — Tank standards, installation requirements, and piping materials.

Sample Questions

These are actual-style questions from the Mississippi Residential Plumbing exam prep bank. Work through them — but don't expect the answers here. Take the free practice exam to check your knowledge.

Question 1 — Isometric Analysis
A residential plumber is sizing a horizontal fixture branch using the IPC. A 3-inch horizontal branch can serve a maximum of how many drainage fixture units?
- A) 48
- B) 12
- C) 20
- D) 72

What it tests: Your ability to pull the correct value from IPC drainage fixture unit tables — the kind of lookup you'll do under time pressure on a real exam.

Question 2 — Piping
You are installing a residential drain line and need to determine the minimum slope for a 4-inch horizontal drainage pipe. What minimum slope per foot is required?
- A) 1/16 inch per foot
- B) 1/2 inch per foot
- C) 1/4 inch per foot
- D) 1/8 inch per foot

What it tests: A fundamental drainage code requirement you'll see applied in multiple contexts across the exam.

Question 3 — Specialty Applications
You are installing a hot water boiler in a residence and need to select an expansion tank. What hydrostatic test pressure must a pressurized expansion tank be capable of withstanding?
- A) Two times the allowable working pressure of the system
- B) Three times the allowable working pressure of the system
- C) Two and one-half times the allowable working pressure of the system
- D) One and one-half times the allowable working pressure of the system

What it tests: Code requirements for expansion tanks — a detail buried in the IRC or IPC that rewards careful tabbing.

Question 4 — Specialty Applications
When performing a percolation test for a subsurface graywater soil absorption system, what is the required depth of gravel or coarse sand that must cover the bottom of the test hole?
- A) 4 inches
- B) 2 inches
- C) 1 inch
- D) 3 inches

What it tests: A specific installation procedure that requires knowing exactly where to look in the code.

Question 5 — Piping
Which standard applies to hubless cast iron soil pipe and fittings used for sanitary and storm drain, waste, and vent piping in residential construction?
- A) ASTM C564
- B) ASTM A74
- C) ASTM A888
- D) CISPI 310

What it tests: Material standards — you need to know which ASTM or CISPI designation applies to which pipe type.

What Types of Questions to Expect

Here's what our practice bank covers across all 12 topic areas — 277 practice questions total:

• General Plumbing Knowledge and Regulations (45 practice questions): Permit procedures, inspection types, code official authority, violations, and plumbing definitions. Mostly straight code-reading.
• Drain, Waste and Vent and Sewers (66 practice questions): DFU load calculations, drain sizing tables, slope rules, cleanout requirements, and DWV pipe material standards. This is where the exam gets technical.
• Isometric Analysis (27 practice questions): Reading riser diagrams, assigning DFU values to fixture groups, accumulating loads downstream, and sizing branches, stacks, and building drains from a diagram.
• Piping, Valves, and Controls (22 practice questions): Pipe material approvals, joint methods by material type, backflow prevention device selection, and water supply system design using fixture unit tables.
• Specialty Applications (18 practice questions): Graywater reuse systems, rainwater collection, percolation testing, subsurface soil absorption sizing, and solar thermal system requirements.
• Fuel Gas (18 practice questions): Gas piping materials, pipe sizing using IFGC capacity tables, pressure testing procedures, combustion air requirements, and appliance clearances.
• Fixtures and Equipment (16 practice questions): Minimum fixture counts by occupancy, installation clearances, flushing device standards, shower liner requirements, and T&P relief valve rules.
• Safety (15 practice questions): PPE requirements, fire extinguisher classifications, excavation and cave-in protection under OSHA 29 CFR 1926, and confined space entry procedures.
• Piping (17 practice questions): Water supply and drainage pipe material standards (copper, CPVC, PEX, PVC, cast iron, ABS), pipe sizing, and separation requirements.
• Water Supply (14 practice questions): Backflow preventer types and applications, flow rate and pressure requirements, distribution pipe sizing, and pressure-reducing valve installation.
• LP Gas (11 practice questions): Propane pipe sizing from IFGC tables, two-stage regulator system design, allowable operating pressures inside buildings, and approved LP-gas pipe materials.
• Fuel Oil (8 practice questions): Tank listing standards (UL 58, UL 80), above-ground and underground installation rules, fill and vent piping termination, and approved oil piping materials.

Study Materials

This is an open-book exam, and these are the approved references. Bring your own copies — you cannot borrow them from anyone at the test center.

Required references:
- IPC 2021 — International Plumbing Code 2021. This is your primary code reference. DWV sizing, fixture requirements, water supply rules — most of the exam lives here.
- IFGC 2018 — 2018 International Fuel Gas Code. Covers all fuel gas and LP gas questions.
- IRC 2021 — International Residential Code for One- and Two-Family Dwellings (2021). Required for residential-specific code questions.
- OSHA 29 CFR 1926 — OSHA Standards for the Construction Industry. Covers the safety topic: excavation, PPE, confined space.

Highly recommended tools:
- Sharpie Tank Highlighters — 12-pack with multiple colors. Use different colors for different topic areas. Bright fluorescent ink that resists smearing once dry. Color-coding your IPC tables is one of the highest-value things you can do before exam day.
- Redi-Tag Permanent Colored Tabs — 100 tabs in 5 colors. Tab every major table and section you'll need to find fast. The permanent adhesive holds well in a well-used code book. This is what separates a 3-minute lookup from a 30-second one.

Study Tips

Give yourself 3–6 weeks. Use the official exam bulletin as your roadmap — it tells you exactly what's tested and in what proportion.

Build fast-lookup skills, not just knowledge. On an open-book exam, you need to find the right table in 30 seconds, not 3 minutes. Tab your books by topic. Practice flipping to DFU tables, slope requirements, and pipe sizing charts until it's automatic.

Set your practice bar at 80%. The real cut score is 70%, but aim higher in practice. Three clean passes at 80% or better gives you a real margin on test day.

Work every question once, then go back. Answer what you know, skip what you don't, and flag it. Don't sink 8 minutes into one question while 10 others sit unanswered. The clock runs the whole time.

Control anxiety with action, not willpower. A little nerves before the exam is normal. If you freeze on a question, pause, take a slow breath, and move on. Come back to flagged questions at the end.

Frequently Asked Questions

How many questions are on the Mississippi Residential Plumbing exam and how long do I have?
The exam has 80 scored questions and you have 240 minutes (4 hours) to complete it.

What is the passing score for the Mississippi Residential Plumbing exam?
You need a minimum score of 70% — that's 56 correct out of 80 questions.

How much does it cost to take the exam?
The exam fee is $120 per examination portion. This applies whether it's your first attempt or a retake, and it's non-refundable and non-transferable.

How do I register?
First, apply with the Mississippi Contractor Licensing Board and wait for eligibility notification from PSI. Once you have that, register through the exam registration page or call PSI at (855) 557-0619.

How long do I have to pass after becoming eligible?
You have 6 months from your eligibility date. You can retest as many times as needed during that window. If 6 months pass without a passing score, you have to reapply with the Board.

Is the Mississippi Residential Plumbing exam open book?
Yes. You can bring your approved reference materials into the test center. They must be your own copies, and you cannot write in them during the exam.

What references are allowed?
The four approved references are: OSHA 29 CFR Part 1926, International Plumbing Code (2021), International Fuel Gas Code (2018), and International Residential Code (2021). You're responsible for bringing your own copies.

Can I use a calculator?
Yes — a silent, non-printing, battery-operated calculator with no alphabetic keyboard and no paper tape is allowed.

What ID do I need on exam day?
One valid, non-expired, government-issued photo ID that also has your signature — a driver's license, state ID, U.S. passport, military ID, Alien Registration Card, or Canadian government ID all work. The name on your ID must exactly match the name on your registration.

When will I get my score?
Immediately. Your result appears on screen as soon as you submit the exam. Pass, and you'll see a performance summary. Don't pass, and you'll get a diagnostic report broken down by topic.

Get Started

You have 80 questions, 4 hours, and four code books. The exam is absolutely passable — but only if you know where to look and how fast to find it. Tab your books, run your practice questions, and set your target at 80% so 70% feels easy.

Start with the free practice exam — 10 questions, no account needed, no commitment. Get a feel for the format and question style. When you're ready to prep in full, the paid practice exam matches the real exam exactly: 80 questions, same time limit, same topic breakdown, with a detailed score report by topic so you know exactly where to focus.

Go get your Mississippi Residential Plumbing license.