Grease Trap Size Calculator
Select a documented code method, enter your inputs, and see the arithmetic. When the required method or device class is unknown, the calculator tells you what to find out first.
Calculate your grease trap size
IPC 2021 §1003.3.7 — gravity grease interceptor
Flow rate in GPM × 30 minutes retention = minimum liquid capacity in gallons.
IPC 2021 §1003.3.5.1 — hydromechanical grease interceptor capacity
The IPC sizes hydromechanical interceptors by flow-through rate (GPM) → required grease retention capacity (pounds). The interceptor must be tested and listed under ASME A112.14.3, ASME A112.14.4, CSA B481.1, PDI G101, or PDI G102.
UPC 2021 Table 1014.3.6 — gravity interceptor by fixture units
Total drainage fixture units (DFU) from connected fixtures → minimum interceptor volume from the code table. A gravity grease interceptor is defined in UPC Chapter 2 as having a 30-minute retention time.
Option 2: Estimate DFU with the fixture picker (UPC Table 702.1)
Select the number of each fixture type connected to the interceptor. DFU values are derived from UPC 2021 Chapter 7 (Table 702.1) as applied by Spokane County, City of Tacoma, and Bainbridge Island. This is an estimate — confirm fixture connections and DFU assignments with the approved plan.
UPC 2021 §1014.2.1 — hydromechanical grease interceptor
Waste-pipe diameter and drainage period (1 or 2 minutes) → required interceptor flow rating from Table 1014.2.1. The interceptor's certified GPM rating must be at least that flow, and its fixture capacity must not exceed 2.5 × the certified GPM rating.
User-supplied values
Enter the flow and time from your authority, engineer, or approved project documents.
- Check your state or province's adopted code — FOG requirements by state or your state regulations page.
- Call the local authority — the health department, water utility, or plumbing division can tell you which code edition and sizing method apply to your project.
- Ask what inputs they need — fixture units, pipe diameter, flow rate, or retention time. The calculator above runs the arithmetic for each method once you know which one applies.
Many local authorities also publish their own sizing worksheets — see the local sizing tools section below.
Scenario result
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Get quotesWhat this calculation does — and does not do
It shows the arithmetic
The result multiplies or looks up the entered values using the cited code method. Inputs, units, method, and assumptions stay visible so you can verify every step.
It does not approve equipment
It does not determine local adoption, amendments, fixture routing, product acceptance, installation conditions, or permits. The local authority and approved plan control.
How the sizing methods work
Two model plumbing codes cover most of the United States. Each has a different procedure for sizing grease interceptors. Canadian provinces use the National Plumbing Code of Canada or a provincial code and size interceptors under CSA B481 — see the Toronto and Metro Vancouver tools below.
IPC — flow × time (gravity) or capacity table (hydromechanical)
The International Plumbing Code (2021) sizes gravity interceptors by multiplying the flow rate in GPM by 30 minutes of retention time (§1003.3.7). Hydromechanical interceptors are sized by a flow-through-to-retention table (§1003.3.5.1). How IPC sizing works →
UPC — fixture units or drainage period
The Uniform Plumbing Code (2021) uses two approaches: Table 1014.3.6 looks up gravity interceptor volume by total drainage fixture units; §1014.2.1 sizes hydromechanical interceptors by waste-pipe diameter and drainage period. How UPC sizing works →
States — and in some states, cities or counties — adopt one of these codes, often with local amendments that change the sizing procedure. The FOG requirements by state tool links to adopted codes. For the difference between gravity and hydromechanical interceptors, see the selection guide.
Grease trap sizing charts (UPC and IPC)
The tables below reproduce the code-published values the calculator uses. A drainage fixture unit (DFU) is a measure of the probable discharge into the sewer system by various types of plumbing fixtures (UPC Chapter 2 definition).
How to calculate grease trap size
- Identify the adopted code — ask the local authority which plumbing code edition (IPC or UPC) and which sizing method apply to your project.
- Determine the device class — gravity grease interceptor (large, buried) or hydromechanical grease interceptor (smaller, indoor, tested under ASME A112.14.3, ASME A112.14.4, CSA B481.1, PDI G101, or PDI G102).
- Gather the inputs — fixture units, pipe diameter, flow rate, or retention time, depending on the method.
- Run the arithmetic or table lookup — use the calculator above or the tables below.
- Confirm with the local authority — the calculation is a planning tool, not a permit or purchase decision.
UPC 2021 Table 1014.3.6 — gravity grease interceptor by DFU
Total drainage fixture units connected to the interceptor → minimum interceptor volume. Source: 2021 Uniform Plumbing Code via UpCodes (Hawaii adoption); rows through 720/7,500 gal cross-verified against Spokane County (2021 UPC) and the 2022 California Plumbing Code.
| Maximum DFU | Minimum Volume (gallons) |
|---|---|
| 8 | 500 |
| 21 | 750 |
| 35 | 1,000 |
| 90 | 1,250 |
| 172 | 1,500 |
| 216 | 2,000 |
| 307 | 2,500 |
| 342 | 3,000 |
| 428 | 4,000 |
| 576 | 5,000 |
| 720 | 7,500 |
| 2,112 | 10,000 |
| 2,640 | 15,000 |
Worked example: small restaurant kitchen
Three-compartment sink (9 DFU) + two-compartment prep sink (6 DFU) + mop sink (3 DFU) + hand sink (2 DFU) = 20 DFU. The ≤21 row of UPC Table 1014.3.6 gives a minimum of 750 gallons for a gravity grease interceptor. Confirm the fixture connections, DFU assignments, and accepted equipment size with the local authority.
UPC 2021 Table 1014.2.1 — hydromechanical grease interceptor by pipe diameter
Waste-pipe diameter and drainage period → required flow rate. The interceptor's certified GPM rating must equal or exceed this flow, and the total fixture capacity must not exceed 2.5 × the certified GPM rating. Table basis: ¼ in/ft slope, Manning's formula, n = 0.012.
| Pipe (in) | Max full-pipe flow (GPM) | 1-minute period (GPM) | 2-minute period (GPM) |
|---|---|---|---|
| 2 | 20 | 20 | 10 |
| 3 | 60 | 75 | 35 |
| 4 | 125 | 150 | 75 |
| 5 | 230 | 250 | 125 |
| 6 | 375 | 400 | 200 |
IPC 2021 §1003.3.5.1 — hydromechanical grease interceptor capacity
Flow-through rate (GPM) → required grease retention capacity (pounds). For flow rates above 100 GPM, the retention capacity is 2× the flow rate in pounds. The interceptor must be tested under PDI G101, ASME A112.14.3, ASME A112.14.4, CSA B481.1, or PDI G102.
| Flow-through (GPM) | Grease retention (lbs) |
|---|---|
| 4 | 8 |
| 6 | 12 |
| 7 | 14 |
| 9 | 18 |
| 10 | 20 |
| 12 | 24 |
| 14 | 28 |
| 15 | 30 |
| 18 | 36 |
| 20 | 40 |
| 25 | 50 |
| 35 | 70 |
| 50 | 100 |
| 75 | 150 |
| 100 | 200 |
IPC 2021 §1003.3.7 — gravity grease interceptor formula
Flow rate (GPM) × 30 minutes retention time = minimum liquid capacity in gallons. Example: 25 GPM × 30 minutes = 750 gallons.
Food-service fixture DFU values
Derived from UPC 2021 Chapter 7 (Table 702.1) as applied by Spokane County, City of Tacoma, and Bainbridge Island. Confirm fixture connections and DFU assignments with the approved plan.
| Fixture | DFU |
|---|---|
| Three-compartment sink (total) | 9 |
| Two-compartment sink (total) | 6 |
| Prep sink (2″ drain) | 4 |
| Hand sink (1½″ drain) | 2 |
| Dishwasher pre-rinse sink | 3 |
| Mop/service sink | 3 |
| Wok sink | 3 |
| Floor drain (2″) | 2 |
| Floor drain (3″) | 6 |
| Floor drain (4″) | 8 |
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Request local quotesLocal sizing tools and worksheets
Some local authorities publish their own sizing worksheets or calculators. These are more specific than the model code because they include local amendments, minimums, and approval steps.
Austin Water — Grease Trap Sizing & Design CriteriaAustin, Texas. Requires approval before purchase. Local fixture-unit method with 100-gallon minimum. [2] Spokane County — Grease Control Device Sizing & Installation Policy
Spokane County, Washington. 2021 UPC-based worksheet; hydromechanical units allowed only at 40 seats or fewer. [3] City of Toronto — Grease Interceptor Installation
Toronto, Ontario. Building permit required. Installation and approval process. [4] Metro Vancouver — Grease Interceptor Sizing Tool
Metro Vancouver, BC. Online sizing tool based on the Food Sector Grease Interceptor Bylaw No. 365, 2023. [5]
Not listed? Ask the local authority directly — many agencies provide sizing guidance that is not published online.
After sizing: cost and installation
Once you have a confirmed size from your local authority:
What grease trap installation costs, with real manufacturer pricing. Installation process checklist
Approval path, documents, and qualified team requirements. Where to install
Site plan, service access, and placement decisions. Interceptor cost by size
Cost ranges for 1,000-gallon and larger gravity interceptors.
For help understanding grease trap sizes, capacities, and what the numbers mean, see the grease trap sizes reference.
Frequently asked questions
What size grease trap do I need?
That depends on the code your local authority adopted (IPC or UPC), the device class (gravity interceptor or hydromechanical), and the inputs the code requires — fixture units, pipe diameter, flow rate, or retention time. Use the calculator above to run a scenario under the applicable method, and confirm the result with your local authority before purchasing.
How do I find out which sizing method my city uses?
Ask the local authority (health department, water utility, or plumbing division) which plumbing code edition is adopted and whether local amendments change the sizing procedure. Many jurisdictions adopt the International Plumbing Code (IPC) or the Uniform Plumbing Code (UPC), sometimes with local modifications. Check FOG requirements by state.
What does GPM mean on a grease trap?
GPM is gallons per minute — the flow rate the device is rated or tested for. A hydromechanical grease interceptor carries a certified GPM rating from testing under ASME A112.14.3 or CSA B481. Gravity interceptors are sized in gallons of liquid capacity, not GPM. The two measurements serve different code methods. What GPM, gallons, and pounds mean.
Can I use a smaller trap and pump it more often?
The adopted code sets the minimum size. Pumping frequency does not replace the sizing calculation. Using equipment smaller than the code and local approval require can result in permit violations, regardless of service schedule.
Does the number of seats or cuisine type decide the size?
The IPC and the UPC's Chapter 10 tables (used in the calculator above) do not use seat counts. The UPC's optional Appendix H (interceptors on private sewage systems, only where adopted) sizes by meals per peak hour, estimated from seating. Some local programs also use seats or meals to decide device type — Spokane County, for example, allows a hydromechanical unit only at 40 seats or fewer and 40 meals per peak hour or fewer. Ask whether your authority uses them.
Do floor drains and dishwashers have to connect to the interceptor?
That is a local code and plan-review question. The IPC and UPC fixture-connection provisions differ, and local amendments can add or remove requirements. Ask your local authority which fixtures must connect for your approved plan.
What happens after I know the required size?
Confirm the size and product with the local authority and a qualified installer. For cost and installation guidance, see the installation cost guide, installation process checklist, and placement guide.
Sources used on this page
International Code Council — IPC 2021
For a gravity grease interceptor, the 2021 International Plumbing Code sizing equation uses the flow rate in gallons per minute multiplied by 30 minutes (§1003.3.7).
Open the official source [1]International Code Council — IPC 2021 §1003.3.5.1
Hydromechanical grease interceptor capacity sized by flow-through rate (GPM) → required grease retention capacity (lbs). For flow rates above 100 GPM, retention = 2× the flow rate.
Open the official source [1b]IAPMO — UPC 2021 Tables 1014.3.6, 1014.2.1, 702.1
Gravity grease interceptor sizing by DFU (Table 1014.3.6), hydromechanical sizing by pipe diameter and drainage period (Table 1014.2.1), and fixture DFU assignments (Table 702.1).
Open the code text — UpCodes rendering, 2021 UPC as adopted in Hawaii (Table 1014.3.6) · Table 1014.2.1Austin Water — Grease Trap Sizing & Design Criteria
Austin, Texas requires grease-trap sizing approval before purchase. Local fixture-unit method with 100-gallon minimum.
Open the official source [2]Spokane County — Grease Control Device Sizing & Installation Policy
Spokane County, Washington publishes a 2021 UPC-based sizing worksheet with local amendments and interceptor minimums.
Open the official source [3]City of Toronto — Grease Interceptor Installation
Toronto requires a building permit to install or replace a grease interceptor in its program.
Open the official source [4]Metro Vancouver — Grease Interceptor Sizing Tool
Metro Vancouver provides an online grease interceptor sizing tool based on the Food Sector Grease Interceptor Bylaw No. 365, 2023.
Open the official source [5]Last fact-checked September 4, 2026. Local authorities, equipment instructions, and site safety procedures control where they apply.
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