PEX Calculator
How much PEX do you need? Add the length of every planned run, then add a waste allowance for cuts, routing and mistakes: total PEX = total run length × (1 + waste % ÷ 100). Enter your runs below to get the footage, the number of coils to buy, and an optional fitting and cost estimate.
PEX Pipe, Fittings & Cost Calculator
Start with the basics. Open Advanced Options for fittings, pricing, water volume, flow, pressure loss, radiant floor and manifold tools.
Important: This calculator provides planning estimates. Actual PEX requirements, pipe sizing, pressure, flow, fittings and installation details depend on the specific plumbing system, manufacturer requirements, local plumbing code and site conditions. For code-required sizing or complex installations, verify the design with a qualified plumbing professional.
Calculation notes: Footage is rounded up to whole feet. Waste is applied to each pipe size separately, and coils are counted per size. Prices are your own entries, so the cost output is an estimate and not a quote.
What Does a PEX Calculator Do?
A PEX calculator turns a rough plan into a shopping list. You enter each pipe run, pick the tubing size, and choose a waste allowance. The tool adds the runs, applies the allowance, and tells you how many coils cover the job.
This one also handles the items that usually get forgotten until the second trip to the store: fittings, valves, crimp rings or clamps, and manifold ports. If you enter prices, it totals the estimated material cost. Four extra tools sit in Advanced Options for people who want more detail: water volume, flow and velocity, pressure drop, and radiant floor tubing.
It does not design your system. It does arithmetic on the numbers you give it, and it says so when a result needs information you have not provided.
How to Calculate How Much PEX Pipe You Need
How do you calculate PEX tubing? Measure every planned run, add the lengths together, then multiply by 1 plus your waste percentage. Total PEX = total run length × (1 + waste % ÷ 100). Round up to a length you can actually buy.
Follow these steps:
- Sketch the water heater, the main shutoff and each fixture. Decide whether you will use trunk-and-branch lines or a manifold with home runs.
- Measure each run along the path the pipe will take, not in a straight line. Include vertical drops and rises.
- Group runs by tubing size, because 1/2-inch and 3/4-inch tubing are bought separately.
- Add a waste allowance for cuts, offcuts and mistakes.
- Compare the total to the coil lengths your supplier sells.
Hot and cold lines to the same fixture are separate runs. A shower with hot and cold supplies counts as two lengths of tubing, so enter both. A manifold system also needs a run for each outlet, which can add up faster than people expect.
How Much PEX Do I Need?
How much PEX do I need? It equals the total of your measured runs plus a waste allowance. There is no standard footage for a bathroom or a house, because layout drives the answer.
These factors change the number the most:
- Number of fixtures. Each fixture adds at least one supply run, and often two (hot and cold).
- Pipe routing. Going around framing, up through floors or across a basement adds footage.
- Run length. Distance from the water heater and main supply is usually the biggest single input.
- PEX size. Sizing does not change the footage, but it splits your total into separate purchases.
- Manifold layout. A home-run system uses more tubing than trunk-and-branch, in exchange for dedicated lines.
- Installation method. Crimp, clamp and expansion systems waste tubing differently.
- Cutting allowance. Clean square cuts, test fits and mistakes all use some tubing.
Use a tape measure on the actual route. If the walls are not open yet, add a margin and enter a higher waste allowance.
PEX Waste Allowance
How much extra PEX should I buy? Many installers plan for some extra tubing, and the right amount depends on the job. Simple, well-measured runs need less. Tight spaces, many direction changes or an inexperienced installer justify more.
The calculator offers 0%, 5%, 10%, 15% and a custom field as planning starting points. They are not rules.
| Situation | Waste tendency |
|---|---|
| Open walls, short, straight runs, exact measurements | Lower |
| Finished walls, unknown routing, long runs | Higher |
| Many bends, offsets or manifold home runs | Higher |
| First PEX project, practicing connections | Higher |
Unused tubing is not wasted money if the leftover coil handles a later repair. Running short mid-job usually costs more than a few extra feet.
PEX Coil Calculation
How many feet are in a PEX coil? PEX coils are commonly sold in lengths such as 100, 300, 500 and 1,000 feet, but availability varies by brand, size and retailer. Check the product listing.
The calculator rounds up to whole coils:
Say you need 462 ft of 1/2-inch PEX and your supplier sells 300 ft coils. 462 ÷ 300 = 1.54, so you buy 2 coils (600 ft) and have about 138 ft left over. A 500 ft coil would cover the job with 38 ft left over. Compare options by entering a different coil length.
Coils are counted separately for each pipe size, since you cannot use 3/4-inch tubing for a 1/2-inch run. Prices per foot also differ between coil sizes, so check whether a larger coil costs less per foot before you decide.
PEX Fitting Calculation
Fittings depend on your layout, not on tubing length. The calculator therefore takes quantities that you count from your plan instead of guessing them.
Common fittings include:
- Couplings join two lengths of tubing, for example when repairing a damaged section.
- 90-degree elbows make sharp turns where bending the tubing would be impractical.
- Tees split a line to serve another branch or fixture.
- Reducers connect different tubing sizes, such as 3/4-inch to 1/2-inch.
- Adapters transition PEX to threaded, sweat or other connections. Male and female threaded adapters are counted separately.
- Shutoff and ball valves isolate fixtures or sections of the system.
A practical way to count: walk your plan from the water heater outward. Count every tee where a branch leaves, every elbow where a line turns, every adapter where PEX meets a fixture stop or other material, and every valve. Then add a few spares of the fittings you use most.
Fitting systems are not interchangeable. Crimp, clamp and expansion fittings use different rings and tools, and compatibility depends on the PEX type and manufacturer. Check the fitting manufacturer's instructions before buying. See PEX fitting types for a comparison.
PEX Material Takeoff
A material takeoff is a complete list of what the job needs. After you press Calculate, the results panel lists tubing by size, then every fitting, valve and accessory you entered, with quantities and prices where provided.
Typical items beyond tubing and fittings:
- Crimp rings, cinch clamps or expansion rings, matched to your fitting system.
- Pipe supports, clips or straps spaced as required by the manufacturer and code.
- Protective plates where tubing passes through studs close to the face of the framing.
- Sleeves where tubing passes through concrete or other materials.
- A manifold and its valves for home-run systems.
- Tools such as a cutter, crimp or clamp tool, or expansion tool, if you do not own them.
Use Copy Results to paste the takeoff into a note or email, or Print Results to take a paper copy to the supplier.
PEX Cost Calculation
How much does PEX cost? Cost depends on tubing size, PEX type, brand, fitting system, coil length, supplier and region. This calculator does not assume prices. Enter your own, and it multiplies them by your quantities.
The estimate separates four cost types:
- Tubing: price per foot × footage, either required or purchased in whole coils.
- Fittings and valves: quantity × unit price for each item.
- Accessories: clamps, rings, supports, manifolds, tools and other materials.
- Labor: an optional flat amount if you are hiring the work.
Material cost is tubing plus fittings and valves plus accessories. Total project cost adds labor. Permits, inspections, water heater work, wall repair and fixture costs are not included unless you add them to the other-materials field.
Pricing the full coils you buy gives a more realistic shopping total than pricing only the footage you use. You can switch between the two in the Prices & labor section.
PEX Pipe Size Considerations
What size PEX should I use? The size depends on the demand the pipe must serve, available pressure, length and local code. 1/2-inch is widely used for individual fixture branches and 3/4-inch for larger branches and mains, but neither is right for every case.
PEX is sold in copper tube sizes (CTS), so the nominal size is a label. It is not the actual inside diameter. Inside diameter also varies by manufacturer and PEX type because wall thickness differs. That matters for flow, which is why the size guide in Advanced Options shows typical values and lets you override them.
| Nominal size | Typical use |
|---|---|
| 3/8 in | Short branches to a single fixture, where code and the manufacturer allow |
| 1/2 in | Common for individual fixture supplies |
| 3/4 in | Larger branches, trunk lines and many water heater connections |
| 1 in | Main and trunk lines in larger homes, or longer high-demand runs |
| 1-1/4 in | Large trunk lines or high-demand buildings |
Is 3/4-inch better than 1/2-inch? It carries more water with less friction, and it also costs more and is harder to route. Using oversized pipe everywhere raises cost and can increase the time it takes hot water to arrive. Sizing is a balance, and code tables or a designer settle it. Read more about PEX pipe sizes.
PEX-A vs PEX-B
PEX-A, PEX-B and PEX-C are named for their cross-linking methods. In general, PEX-A is more flexible and is often used with expansion fittings. PEX-B is somewhat stiffer and is commonly used with crimp or clamp fittings. Pricing, availability and fitting compatibility vary by manufacturer. Do not assume that all three behave the same in every respect. Our guide to PEX-A vs PEX-B covers the differences.
PEX Manifold Considerations
A manifold distributes water from a central point to dedicated lines, called home runs, that each serve one fixture or a small group. Compared with trunk-and-branch plumbing, a manifold uses more tubing but gives you individual shutoffs and often more stable pressure when two fixtures run together.
Plan ports like this:
- A fixture that needs hot and cold uses one outlet on the hot manifold and one on the cold manifold.
- A cold-only line, such as a toilet or hose bibb, uses one cold outlet.
- Each radiant loop uses one supply and one return connection.
- Spare ports leave room for later additions.
The manifold tool calculates active ports, adds the spare allowance you choose, and compares the total with the manifold you are considering. No single port count is correct for every home. See PEX manifold systems for layout ideas.
Radiant Floor PEX Calculation
How do you calculate radiant floor PEX? Multiply heated area (sq ft) by 12, then divide by tubing spacing in inches. That gives feet of tubing in the heated area. Add the supply and return distance to the manifold for each loop, then add waste.
Example: a 240 sq ft floor at 12-inch spacing needs about 240 ft of tubing in the floor. At 8-inch spacing it needs about 360 ft. At 6-inch spacing it needs about 480 ft.
Loop count follows from the maximum loop length. Each loop also carries a lead to the manifold and back, so the usable length per loop equals the maximum length minus twice the one-way distance. Loops = ceiling(heated tubing ÷ usable length per loop). The calculator splits the tubing into equal loops and adds the leads.
How far apart should radiant PEX tubing be? Spacing of 6 to 12 inches is common. Closer spacing delivers more heat per square foot and uses more tubing. The right value comes from a heat-loss calculation, floor covering, water temperature and the manufacturer's loop limits. This tool does not calculate heating load or BTU output because that needs heat-loss data.
How Accurate Is a PEX Calculator?
The arithmetic is exact. The result is only as good as your measurements and your waste choice. A calculator cannot see your framing, your obstructions or your mistakes.
- Measurements. Straight-line distances underestimate real routes.
- Waste. Presets are planning starting points, not universal figures.
- Inside diameters. Typical values are used unless you override them. Brands differ.
- Pressure drop. The Hazen-Williams result covers friction in straight pipe. Fittings, valves, water temperature and elevation change the real figure.
- Code. Plumbing code sets minimum sizes and installation rules. This tool does not apply them.
When an input is missing, the tool asks for it instead of inventing a value. For code-required sizing, permits or complex installations, verify the design with a licensed plumber.
PEX Calculator Formulas
Total tubing
Waste-adjusted tubing
Coil count
Unused tubing = coils × coil length − required tubing
Approximate water volume
Inside the tube, water fills a cylinder. With inside diameter d in inches and length L in feet:
Gallons = in³ ÷ 231
Liters = gallons × 3.785
For 100 ft of tubing with a 0.485 in inside diameter, that is about 0.96 gal (3.6 L).
Velocity
Friction loss (Hazen-Williams)
Friction loss = loss per foot × (pipe length + fitting equivalent length)
Static pressure change = 0.433 psi × elevation rise (ft)
Q is flow in gpm, d is inside diameter in inches, and C is the roughness coefficient. The tool starts with C = 150, a figure commonly used for smooth plastic pipe, and you can change it to match manufacturer data. Hazen-Williams does not model temperature, so treat results as estimates.
Radiant floor tubing
Loops = ceiling(heated tubing ÷ (max loop length − 2 × one-way lead))
Total tubing = (heated tubing + 2 × lead × loops) × (1 + waste % ÷ 100)
Manifold ports
Worked Example
A homeowner is repiping a bathroom and measures each supply run along its planned path:
| Run | Length |
|---|---|
| Sink | 35 ft |
| Toilet | 30 ft |
| Shower | 42 ft |
| Tub | 45 ft |
| Base tubing | 152 ft |
With a 10% planning allowance: 152 × 1.10 = 167.2 ft. The calculator rounds up to 168 ft. With 100 ft coils, that is 2 coils (200 ft) and about 32 ft unused. With a 300 ft coil, it is 1 coil and 132 ft unused.
These distances are only an example. Your layout, routing and fixture count will be different.
Related PEX Resources
- What PEX is and how it works
- How to crimp PEX connections
- How to cut PEX pipe cleanly
- PEX plumbing tools you need
- PEX compared with copper
- PEX plumbing cost breakdown
- Repiping a house with PEX
- Common PEX concerns explained
Frequently Asked Questions
How do I calculate how much PEX I need?
Measure every run along its actual path, add the lengths, and multiply by 1 plus your waste percentage. For example, 152 ft with a 10% allowance gives 167.2 ft, which you round up before buying.
How many feet of PEX do I need?
It depends on your layout. Add up the lengths of all hot and cold runs for every fixture, then add an allowance for waste. No standard footage applies to every home.
How much PEX should I buy for a bathroom?
Measure the hot and cold supply runs from your water source to each fixture and add them up. The bathroom preset adds sink, toilet, shower and tub so you can enter real lengths. Distance from the water heater changes the total more than the fixture count does.
How much PEX do I need for a whole house?
Treat it as many runs: water heater, each bathroom, kitchen, laundry and outdoor connections. Enter each run and size. Trunk-and-branch systems use less tubing than manifold home runs, but the manifold gives dedicated lines.
How much extra PEX should I buy?
Many people plan for some extra, such as 5% to 15%, depending on how simple the routing is. There is no single correct percentage. Use more when measurements are uncertain or the layout is complex.
What is the formula for PEX tubing?
Required tubing = total run length × (1 + waste % ÷ 100). To buy coils, divide by the coil length and round up.
What size PEX should I use?
It depends on demand, pressure, length, elevation and local code. 1/2-inch is common for fixture branches and 3/4-inch for larger branches and mains, but confirm with code tables or a plumbing professional.
Is 1/2-inch or 3/4-inch PEX better?
Neither is better in general. 3/4-inch has more flow area and lower friction loss, but costs more and is bulkier. Use the size that fits the load and code.
How many fittings do I need for PEX?
Count them from your plan: one tee per branch, one elbow per sharp turn, one adapter where PEX meets another material, and a valve per shutoff. Fittings depend on layout, not on tubing length.
How do I calculate PEX fittings?
Walk your plan from the water heater outward and tally each tee, elbow, coupling, adapter and valve. Enter the totals in Advanced Options. Add a few spares of the types you use most.
How much does PEX plumbing cost?
Cost varies by brand, size, supplier, region and fitting system. Enter your own per-foot and per-fitting prices and the calculator estimates tubing, fittings, accessories and total cost.
How long can a PEX run be?
There is no single maximum. The limit depends on tubing size, flow rate, available pressure, elevation, fittings and code. The pressure drop tool estimates friction loss for a specific run.
How much water does PEX tubing hold?
It depends on inside diameter, which varies by brand. As an example, 100 ft of tubing with a 0.485 in inside diameter holds about 0.96 gal. Use the water volume tool with your own diameter for a closer figure.
How much PEX is needed for radiant floor heating?
Heated area × 12 ÷ spacing in inches gives feet of tubing in the floor. Add the supply and return runs to the manifold for each loop, then waste.
How far apart should radiant PEX tubing be?
6 to 12 inches is common. Closer spacing gives more heat per square foot and uses more tubing. A heat-loss calculation and the manufacturer's data should set the final value.
How many PEX loops do I need?
Divide heated tubing by the usable length per loop, which is the maximum loop length minus the supply and return leads, and round up. The radiant tool does this for you.
How do I calculate PEX coil requirements?
Divide the required footage by the coil length and round up to whole coils. Do this separately for each tubing size. Subtract the footage you need from the footage you buy to see what is left over.
