Lawrence residents, start measuring your trash.

City commissioners on Tuesday agreed to spend $885,490 to order enough trash carts to outfit every single-family home in the city with a plastic cart. But commissioners also agreed to a new rate plan that will cut the trash bills of households that can routinely fit their trash into a small, 35-gallon cart.

“It seems to me we want to create an incentive where people aren’t putting so much trash in the landfill,” said City Commissioner Mike Amyx.

Commissioners at their weekly meeting unanimously went against a staff recommendation and created a new rate system that provides a $1.50-per-month reduction in trash rates for people who agree to use the 35-gallon cart.

Under the new rate plan, residents will pay $13.44 per month for trash service if they use a 35-gallon cart. Currently, the base rate for trash service — with no cart — is $14.94 per month.

Under the new system, which is expected to begin by late October, all single-family households will be required to use a cart. City leaders believe most households will use a 65-gallon cart. The monthly rate for the 65-gallon service will be $14.94 per month, which is equal to the current base rate.

Households who use a 95-gallon cart will pay $16.94 per month.

Commissioners increased that 95-gallon rate by $1 over what staff members had recommended. Commissioners then reduced the 35-gallon rate by $1 compared with what staff members had recommended.

The city is still proposing that residents “occasionally” will be allowed to set out extra bags of trash that won’t fit into their wheeled carts. But commissioners said the city likely will have to be strict on the enforcement for those taking advantage of the reduced 35-gallon rate.

“We need to write some type of policy that if this is abused, it will be taken away,” said City Commissioner Aron Cromwell.

In other news, commissioners agreed to a 20-month, $233,800 lease to move the Lawrence Public Library into the former Borders bookstore, 700 N.H., while the main library undergoes a $19 million expansion.

The move is expected to happen by early January. Commissioners said they expect the move to help save on construction costs at the library.