Package volume at multifamily and community-scale properties has climbed sharply over the past five years, and 2026 is on pace to set another record. The average American household now receives more than 100 packages a year, and dense residential properties routinely see spikes during holiday seasons, back-to-school windows, and every major online retail event. For property managers, HOA boards, and developers ordering new cluster box units, this shift has turned parcel locker sizing from a minor spec into a decision that directly affects tenant satisfaction, delivery reliability, and long-term operating cost.

Cluster box units, commonly called CBUs, are the centralized mail delivery solution the United States Postal Service recommends for new residential developments of three units or more. Every USPS-approved CBU includes a mix of tenant compartments for standard mail and larger parcel locker compartments for packages. What varies across models and manufacturers is how many parcel lockers ship per unit, how those lockers are sized, and how easily additional locker capacity can be added later. Getting the ratio right the first time is far cheaper than retrofitting.

At US Post Company, we work with property managers, developers, HOA boards, and general contractors nationwide on CBU sizing decisions. This guide walks through how we recommend matching parcel locker capacity to actual package volume, what the current USPS standards require, and how the three CBU brands we carry (Florence, Postal Products Unlimited, and Salsbury Industries) approach parcel locker design.

Why Parcel Locker Sizing Matters More in 2026

The economics of centralized mail delivery only work when packages reliably land inside the CBU. When parcel lockers fill up, one of two failure modes takes over. Either the carrier leaves packages loose at the base of the unit (creating theft and weather-damage risk), or the carrier stops attempting parcel delivery entirely and routes packages back to the local post office for tenant pickup. Both outcomes generate tenant complaints, and the second one quietly shifts a service the property was designed to provide back onto individual residents.

Undersized parcel locker capacity is now the single most common CBU complaint we hear from property managers taking over existing installations. A CBU sized to 2018 package volumes often runs out of parcel lockers by late morning on a busy delivery day in 2026. A CBU sized correctly for current volumes has capacity to spare and reduces carrier friction, which in turn improves delivery consistency.

Understanding Parcel Locker Compartments

Every USPS-approved cluster box unit ships with a fixed complement of tenant mail compartments and parcel locker compartments. Parcel lockers are the taller, deeper compartments (typically located at the top or bottom of the unit) that hold packages too large for a standard tenant mail slot. When a carrier places a package inside a parcel locker, they insert the parcel locker key into the corresponding tenant's mail compartment. The tenant retrieves the key, opens the parcel locker, removes the package, and returns the key to the carrier the following business day.

The key mechanics are worth understanding because they influence sizing. A CBU with four parcel lockers can handle four packages at a time, per delivery cycle. If more than four packages arrive on the same day, the carrier has to make a choice about what fits and what does not. The United States Postal Service (USPS) sets minimum parcel locker dimensions, but many properties benefit from oversized parcel lockers or additional locker capacity beyond the USPS minimum.

Recommended Parcel Locker Ratios by Property Type

The USPS baseline for CBU-served residential properties is one parcel locker for every five tenant compartments. This ratio was set when average annual per-household package volume was well under 50 shipments. For most 2026 installations, we recommend a higher ratio depending on property type.

• Standard multifamily rental (garden-style, 4-40 units): aim for a 1:4 parcel locker to tenant compartment ratio, with at least one oversized locker per unit for larger boxes
• Student housing, young professional properties, and first-time homebuyer developments: aim for a 1:3 ratio, as these demographics have the highest per-capita package volume
• 55+ active adult and retirement communities: a 1:5 ratio is typically sufficient, as package volume runs lower per tenant
• Luxury or high-income multifamily: aim for 1:3 with multiple oversized lockers, as premium-priced tenants receive higher package volumes and expect reliable delivery
• HOA neighborhoods with single-family or townhome ownership: aim for 1:4, with attention to holiday-season peak capacity
• Mixed-use commercial and residential: add capacity for commercial tenant package volume on top of residential baseline

These are starting points. Properties with a delivery service like a local grocer, a subscription box concentration, or a large small-business tenant may need to size higher.

Calculating Actual Package Volume Before Ordering

The most reliable way to size parcel locker capacity is to measure. For existing properties, ask your current mail carrier to spend a week logging how many packages the property receives per delivery day and how many fit inside available parcel lockers. Divide the average daily package count by the number of parcel lockers currently available to calculate turnover rate. A healthy CBU installation runs at 60 to 75 percent parcel locker utilization on an average day, leaving headroom for peak days.

For new construction or greenfield HOA developments, use the following back-of-envelope calculation as a starting point:

1. Estimate 2 to 3 packages per household per week as the current national average
2. Multiply by the number of units served by the CBU
3. Divide by 5 (delivery days per week) to get average daily package volume
4. Multiply by 1.5 to account for peak days and holiday seasons
5. Divide by 0.7 (target utilization rate) to determine required parcel locker capacity

For a 24-unit garden apartment building, this works out to approximately 15 parcel lockers needed on peak days. Since standard CBU models typically ship with 1 to 4 parcel lockers per unit, a 24-unit property may need multiple CBUs or a larger F-spec CBU to reach the target.

Sizing Pitfalls to Avoid

Two common mistakes recur across the properties we consult on. The first is buying the smallest CBU that technically covers the number of tenant compartments needed. This approach ignores parcel locker capacity entirely, and it inevitably leads to undersized parcel service and tenant complaints within the first year of occupancy.

The second mistake is buying only standard-size parcel lockers when larger box-format packages are common. A parcel locker sized to hold a paperback book box will not hold an Amazon Prime shipment of a stand mixer or a case of bottled water. Every CBU installation should include at least one oversized parcel locker capable of holding a standard 16-inch cube box, and larger properties benefit from having two or more oversized options.

Oversizing has costs as well. Every additional parcel locker takes footprint that could otherwise hold tenant compartments, so a property with more parcel lockers than needed will require a larger CBU (or multiple CBUs) to serve the same number of tenants. Balance is the goal, not maximum capacity.

USPS Approved Compliance and Approval

All new residential CBU installations must meet USPS specifications and pass USPS approval before the local carrier will service the unit. This standard defines minimum tenant compartment dimensions, minimum parcel locker dimensions, height and reach requirements, and door and lock hardware specifications. The three CBU brands we carry (Florence, Postal Products Unlimited, and Salsbury Industries) are all USPS-approved and meet or exceed compliance requirements out of the box.

Where developers and property managers occasionally run into trouble is with retrofits or custom configurations. Adding an aftermarket parcel locker to a CBU that was not designed for expansion can void USPS approval, and unapproved units may not be serviced. When in doubt, order additional CBUs rather than modifying existing hardware.

CBU Brand Comparison for Parcel Locker Capacity

The three USPS-approved CBU brands we carry each take a different approach to parcel locker configuration.

Florence Manufacturing offers CBU models in tenant counts from 4 to 16, with parcel locker counts scaling proportionally. Florence F-spec CBUs are the most common installation in mid-size multifamily and HOA properties, and they offer a strong balance of standard and oversized parcel locker options. Florence units are available in multiple color finishes to match property architecture.

Postal Products Unlimited (PPU) specializes in CBUs designed for higher parcel volume out of the box. PPU units frequently ship with a higher parcel-locker-to-tenant ratio than Florence equivalents, making them a strong choice for properties expecting heavy package volume. PPU offers gray, dark bronze, and other finishes suited to modern commercial and multifamily aesthetics.

Salsbury Industries offers CBUs across the residential and light-commercial spectrum, including cluster box units in 4 through 16 tenant configurations. Salsbury also carries dedicated outdoor parcel lockers (OPLs) that can be installed alongside an existing CBU when additional package capacity is needed without replacing the primary unit.

All three brands work with standard USPS arrow locks and integrate cleanly into existing centralized delivery zones. The best fit depends on parcel volume expectations, aesthetic requirements, and whether the installation is new construction or a retrofit.

Adding Parcel Locker Capacity to Existing Installations

For properties already operating a CBU that is running short on parcel locker capacity, three practical options exist without replacing the primary unit.

• Install a dedicated outdoor parcel locker (OPL) unit alongside the existing CBU. Salsbury OPLs and Florence standalone parcel locker units are designed for this use case
• Add a second CBU nearby if the property has grown in size or package volume beyond the original unit's capacity
• For very high-volume properties, add a smart parcel locker system that supplements the USPS-serviced CBU with a package-only unit accepting deliveries from FedEx, UPS, and Amazon

Each option has trade-offs in cost, permitting, and USPS approval, and the right choice depends on the specific property's constraints.

Signs Your Current CBU Needs a Parcel Locker Upgrade

Property managers should watch for these indicators that current parcel locker capacity is no longer adequate:

• Tenants regularly report packages left at the base of the CBU rather than inside parcel lockers
• Tenants receive frequent USPS pickup notifications for packages routed to the post office instead of the CBU
• Package theft complaints increase, particularly during peak delivery seasons
• Mail carrier reports (formal or informal) that parcel lockers are consistently full on arrival
• Package deliveries from carriers other than USPS accumulate in leasing offices or common areas

Any two or more of these indicators typically justify a capacity review, and three or more usually justify adding capacity.

How US Post Company Helps

US Post Company is an authorized dealer for Florence, Postal Products Unlimited, and Salsbury Industries, and we support property managers, developers, HOA boards, and general contractors on CBU sizing decisions daily. If you are planning a new installation, expanding an existing property, or troubleshooting parcel service problems on a CBU already in place, our team can review your specific property details and recommend the right unit size and brand for your package volume.

Contact us at 800-977-2626 or service@uspostmailbox.com to discuss your CBU parcel locker sizing questions. We ship USPS-approved cluster box units nationwide and provide sizing guidance at no cost as part of every quote.