Fixture Unit Load Calculator

Size your water service by adding up fixture units. Get the right pipe sizes and water meter without pressure problems or oversized pipes. Works in Imperial and metric units.

Add Fixtures

Building Type

Plumbing Code

Fixture Type

Quantity

Added Fixtures

No fixtures added yet

Fixture Unit Reference (IPC)

Fixture	Cold	Hot	Total
Bathroom Sink	0.5	0.5	1
Kitchen Sink	1	1	1.5
Laundry Sink	1	1	1.5
Bathtub	1	1	2
Shower	1	1	2
Tub/Shower Combo	1	1	2
Water Closet (Toilet)	2.5	0	2.5
Bidet	1	1	2
Dishwasher	0	1.5	1.5
Washing Machine	1	1	2
Bar Sink	0.5	0.5	1
Utility Sink	1	1	1.5
Hose Bib	2.5	0	2.5
Floor Drain	1	0	1

Professional Applications

Water Service Sizing

• Main water line sizing
• Water meter selection
• Pressure loss calculations
• Branch line sizing

System Design

• Commercial building design
• Multi-family housing
• Hotel and restaurant sizing
• Hospital and institutional

Code Compliance

• IPC vs UPC fixture unit differences
• Local code requirements may vary
• Permit applications
• Inspection preparation

Frequently Asked Questions

What exactly are fixture units and why do we use them?

Fixture units are basically a way to standardize how much water different plumbing fixtures actually use. Instead of trying to add up every possible flow rate, the codes assign each fixture a "unit" value. A regular bathroom sink gets 1 fixture unit, while a toilet gets 2.5-3 units. This system works because it accounts for the fact that not everyone uses all their fixtures at the same time.

Why are IPC and UPC fixture unit values different?

The International Plumbing Code (IPC) and Uniform Plumbing Code (UPC) use different values because they were developed independently and have different philosophies. UPC tends to be more conservative with higher fixture unit values, especially for things like kitchen sinks and washing machines. If you're working in California, Nevada, or parts of the West, you're probably dealing with UPC. Most other places use IPC.

How do I know what building type to select?

It's all about usage patterns. Residential buildings have the lowest simultaneous usage - families don't typically run every fixture at once. Commercial buildings like offices have moderate usage, while institutional buildings like hospitals or schools have the highest because they're designed for constant, heavy use. When in doubt, go with the higher category for safety.

Can I use this calculator with metric measurements?

Absolutely. Just hit the metric toggle button and the flow rates will show in liters per minute instead of gallons per minute, and pipe sizes will be in millimeters. The fixture unit values stay the same since they're dimensionless - a toilet is still 2.5 fixture units whether you're thinking in gallons or liters. Perfect for international projects.

What's this Hunter's Curve thing the calculator mentions?

Hunter's Curve is an old engineering formula that converts fixture units into actual flow rates. It's based on the probability that multiple fixtures will be used simultaneously. Basically, it assumes that the more fixtures you have, the less likely they'll all be running at once. The curve prevents you from oversizing pipes by adding up every single fixture's maximum flow rate.

Should I size my hot and cold water systems the same?

Not usually. Hot water demand is typically lower than cold water because not every fixture uses hot water (toilets, outdoor spigots), and when fixtures do use hot water, it's often mixed with cold. That's why the calculator shows separate cold and hot water fixture unit totals. Your hot water piping can often be smaller than your cold water mains.

Why does the calculator recommend different pipe sizes than my flow rate suggests?

Because pipe sizing isn't just about flow capacity - it's about keeping water velocity reasonable. Most codes limit velocity to 8 feet per second (2.4 m/s) to prevent erosion and noise. A 1-inch (25mm) pipe might technically handle more flow, but if the water's moving too fast, you'll get hammer, erosion, and angry customers. The calculator factors in these velocity limits.

How accurate are these calculations for real-world applications?

Pretty accurate for typical buildings, but they're conservative by design. The fixture unit system has been around since the 1940s and has proven reliable. That said, special situations like restaurant kitchens, medical facilities, or buildings with unusual usage patterns might need additional analysis. Always check local codes too - some jurisdictions have their own modifications.

What's the difference between estimated flow and peak demand?

Estimated flow is what you'd typically see during normal use, while peak demand adds a safety factor for those times when usage spikes. Water meters and service lines are usually sized for peak demand because the water utility needs to maintain pressure even during high-demand periods. Your distribution piping inside the building can often be sized for the estimated flow.

Do I need to include fixtures that aren't installed yet?

For rough-in work, absolutely. Include everything that's planned for the space, even if it's not going in immediately. It's much cheaper to size pipes correctly upfront than to tear apart walls later. For renovation work where you're only adding a few fixtures, you can usually just calculate the additional load and verify your existing service can handle it.

What about special fixtures like irrigation systems or fire sprinklers?

Those typically get calculated separately. Irrigation systems have their own flow requirements that don't follow fixture unit patterns, and fire protection systems are a whole different calculation based on occupancy and building size. Include standard plumbing fixtures in your fixture unit calculation, but handle special systems with their own design methods and separate water services if needed.

Can I use fixture units to size my water service and meter?

Absolutely - that's exactly what the water utility and health department want to see. Convert your total fixture units to GPM using the code tables, then show that your water service line and meter can handle that flow. Most places require proof that you can deliver the calculated demand at minimum pressure (usually 15-20 PSI) to the farthest fixture. It's part of getting your construction permits approved.

Complete Your Building Water System Design

Fixture unit loads determine your entire building's water system requirements. Use these calculators for comprehensive design:

Friction Loss•Hot Water Recirculation•Expansion Tank Sizing•Unit Converter