Calculate fixture load
Start with fixture values, then total the fixtures connected to the pipe section you are checking.
Plumbing Calculator Hub
Free Plumbing Calculators and Drainage Sizing Guides
Calculate drainage fixture units, estimate sewer fall, compare fixture values, and review 3-inch and 4-inch pipe-sizing questions. The hub also links to bathroom, ADU, drainage-layout, fitting, UPC, and IPC guides so you can move from fixture count to the correct code review.
Calculate Drainage Fixture UnitsCalculate Sewer SlopeLook Up Fixture DFUsReview 3-Inch Pipe Capacity
Common starting points: bathroom DFU examples, toilet DFU, lavatory sink DFU, kitchen sink DFU, shower DFU, ADU plumbing, and IPC vs UPC.
Browse Plumbing Tools by Task
Choose the task that matches your question. Every destination below is a direct crawlable link to a calculator or detailed plumbing reference page.
Check a specific fixture
Use the dedicated fixture guides for direct answers and links back to the full chart and calculator.
Review drain or sewer sizing
After calculating DFUs, identify the pipe section, check slope, and review the relevant pipe-size guide.
Confirm code and layout rules
Check the applicable code basis before relying on DFU, venting, fitting, or pipe-sizing assumptions.
A Practical Plumbing Calculation Workflow
Most drainage questions follow the same sequence: total the connected fixture load, check the available pipe slope, identify the pipe section, and then review the correct sizing table and local code requirements.
1. Total the Fixture Load
Use the DFU calculator to estimate total drainage fixture units for toilets, sinks, showers, tubs, kitchens, laundry, and ADUs.
2. Check Available Slope
Use the sewer slope calculator to estimate pipe fall over distance and compare common slope assumptions.
3. Review the Pipe Section
Identify whether you are checking a branch, stack, building drain, or building sewer, then open the matching sizing reference.
Plumbing Calculators
These interactive tools help with early plumbing calculations, including drainage fixture units and sewer slope.
Interactive Calculator
DFU Calculator
Enter fixture quantities and total drainage fixture units for toilets, lavatories, showers, tubs, kitchens, laundry rooms, bathrooms, and ADUs using UPC or IPC planning values.
Best for: Estimating the fixture load connected to a branch drain, building drain, or sewer.
Open DFU Calculator →Interactive Calculator
Sewer Slope Calculator
Calculate pipe fall over a measured run and compare common drainage slopes such as 1/4 inch per foot and 1/8 inch per foot.
Best for: Checking required fall, available elevation, and early gravity-drain layout feasibility.
Open Sewer Slope Calculator →DFU Calculator and Fixture Unit Guides
Use these DFU resources to calculate fixture-unit totals, compare UPC and IPC values, and estimate loads for bathrooms, toilets, laundry areas, kitchens, and ADUs.
DFU Reference
DFU Chart by Fixture
Look up common UPC and IPC drainage fixture-unit values for toilets, lavatories, showers, tubs, kitchen fixtures, washers, floor drains, and other fixtures.
Best for: Finding an individual fixture value before using the DFU calculator.
Open DFU Chart by Fixture →DFU Basics
What Is a DFU in Plumbing?
Learn what drainage fixture units measure, how fixture values are added, and how DFUs relate to drain and sewer sizing.
Best for: Understanding fixture units before using the DFU chart or calculator.
Open What Is a DFU in Plumbing? →Bathroom Fixture Loads
Bathroom DFU Guide
Compare simplified DFU totals for half bathrooms, full bathrooms, primary bathrooms, double vanities, separate tubs, showers, and bidets.
Best for: Estimating a bathroom group before adding it to a larger house or sewer total.
Open Bathroom DFU Guide →Toilet Fixture Units
Toilet DFU Guide
Check common private-use and public-use toilet DFU values and understand why UPC and IPC assumptions may produce different totals.
Best for: Answering how many drainage fixture units a toilet contributes.
Open Toilet DFU Guide →Lavatory Fixture Units
Lavatory Sink DFU Guide
Review the common DFU value for a bathroom lavatory and how the sink is considered within a bathroom group.
Best for: Adding vanity or bathroom-sink loads to a fixture count.
Open Lavatory Sink DFU Guide →Kitchen Fixture Units
Kitchen Sink DFU Guide
Review the common residential kitchen-sink DFU value and how dishwashers, food-waste disposers, venting, and code assumptions affect drainage planning.
Best for: Answering how many drainage fixture units a residential kitchen sink contributes.
Open Kitchen Sink DFU Guide →Shower Fixture Units
Shower DFU Guide
Review standard shower DFU values and the additional questions raised by custom showers, multiple heads, large drains, and unusual layouts.
Best for: Adding a shower to a bathroom or branch-drain calculation.
Open Shower DFU Guide →ADU Planning
ADU Plumbing DFU Guide
Estimate ADU fixture loads and review how an accessory dwelling unit may affect a shared building drain, sewer lateral, or existing house total.
Best for: Planning a new ADU, guest suite, conversion, or shared sewer connection.
Open ADU Plumbing DFU Guide →Pipe Sizing and Drainage Layout References
Use these pipe sizing and drainage layout references after you calculate DFUs. Pipe size, slope, fitting selection, pipe orientation, developed length, and local code requirements can all affect the final design.
Pipe Sizing
3-Inch Pipe DFU Capacity Guide
Review how allowable load on 3-inch drainage piping changes with slope, horizontal versus vertical orientation, pipe location, and adopted code.
Best for: Checking whether a 3-inch branch, stack, building drain, or sewer needs closer review.
Open 3-Inch Pipe DFU Capacity Guide →Pipe Sizing
4-Inch Sewer Capacity Guide
Review 4-inch sewer planning considerations for larger homes, multiple bathrooms, ADUs, additions, remodels, and future fixture loads.
Best for: Evaluating a larger building sewer or shared residential lateral.
Open 4-Inch Sewer Capacity Guide →Drainage Layout
Building Drain vs Building Sewer
Identify where the building drain ends and the building sewer begins, and why that distinction changes which sizing table, slope, and cleanout rules apply.
Best for: Applying a DFU total to the correct portion of the drainage system.
Open Building Drain vs Building Sewer →Drainage Fittings
Sanitary Tee vs Wye
Compare sanitary tees, wyes, and combination fittings for drainage and vent layouts, including common vertical and horizontal uses.
Best for: Choosing the fitting type that matches the direction and function of flow.
Open Sanitary Tee vs Wye →Plumbing Code Reference Guides
Use these code guides to understand whether your project is being reviewed under UPC, IPC, state code, or local amendments.
Code Comparison
IPC vs UPC Plumbing Code
Compare IPC and UPC approaches to DFUs, drain sizing, venting, wet venting, trap arms, cleanouts, and fixture grouping.
Best for: Understanding why the same plumbing layout can produce different results under different codes.
Open IPC vs UPC Plumbing Code →Code Lookup
State Plumbing Code Guide
Find a starting point for determining whether a state or local jurisdiction uses UPC, IPC, a state-specific plumbing code, or local amendments.
Best for: Choosing the correct code basis before using fixture values or sizing references.
Open State Plumbing Code Guide →What These Plumbing Calculators Help With
- Calculating drainage fixture units for plumbing projects.
- Estimating bathroom, kitchen, laundry, and ADU fixture loads.
- Checking whether a 3-inch or 4-inch sewer needs review.
- Estimating sewer slope and fall over distance.
- Comparing UPC and IPC fixture-unit assumptions.
- Preparing better questions for plumbers, designers, inspectors, or permit reviewers.
What They Do Not Replace
These plumbing calculators are for early planning and education. They do not replace the adopted plumbing code, local amendments, permit review, field conditions, professional design, or inspection requirements.
Final pipe sizing can depend on pipe slope, developed length, branch layout, stack configuration, venting, wet venting, cleanouts, fixture type, public versus private use, and the authority having jurisdiction.
Common Plumbing Calculator Questions
Which plumbing calculator should I use first?
Start with the DFU calculator when you need to estimate fixture load. Use the sewer slope calculator when you need to calculate pipe fall over a run. After that, review the pipe-sizing and code guides that match the actual pipe section and jurisdiction.
Does BuildCalc have a pipe sizing calculator?
BuildCalc currently provides an interactive DFU calculator and sewer slope calculator, plus crawlable reference guides for 3-inch pipe, 4-inch sewer, building drains, building sewers, UPC, and IPC. Final pipe sizing still requires the correct adopted code table and project conditions.
Can DFUs alone determine drain or sewer size?
No. DFUs estimate fixture load, but pipe diameter, slope, horizontal versus vertical orientation, developed length, venting, cleanouts, fixture grouping, and local amendments also affect the result.
Should I use UPC or IPC values?
Use the plumbing code adopted by the authority having jurisdiction for the project location. A state or local jurisdiction may use UPC, IPC, a state-specific code, or amendments to a model code.
Need help with a plumbing project?
BuildCalc can help you organize your fixture list, DFU estimate, pipe sizing questions, and code assumptions before you talk with a plumber, designer, or building department.
Important Planning Reminder
BuildCalc tools are intended for education, estimating, and early project planning. Always verify fixture-unit values, sewer sizing, pipe slope, venting, cleanout requirements, materials, inspections, and permit requirements with the authority having jurisdiction for your project.