Trim and Molding Calculator

How to Estimate the Amount of Trim Needed

Installing trim can improve the look of any room. Trim can be used to help make the transition between walls and ceilings more finished. Trim can also help frame windows and doors, cover unfinished wall areas, or help add decorative elements to a room.

Estimating the amount of trim moldings needed to complete a room involves finding the length of the area you want to install trim in feet.

Calculate Baseboard, Chair Rail, and Crown Moldings

Baseboard, chair rail, and crown moldings can all be calculated using the same method. Moldings are all sold in specific lengths but are generally quoted in price by the linear foot.

You will need to get the linear feet of the area you want to install them on, then determine the length of the trim piece to determine how many pieces of trim will be required, as well as the cost. Use our length unit conversion tools to convert length measurements to feet.

Measure the length of each area you will install the trim on. For long walls, this is easy – just get the total length of the wall. For bump-outs, jogs, or walls with interruptions, you will need to measure each section individually, then add them together.

If the areas are small, measure all of the lengths on this wall in inches. After you add them together, divide by 12 and round up to the nearest whole number to get the total number of linear feet.

Moldings are sold by the linear foot or in lengths of generally 8′. Some moldings may be sold in other lengths; if this is the case, be sure to get the exact length of that molding. If your chosen molding is sold by the linear foot, take the linear footage you calculated when measuring, add one extra foot for length, and purchase this amount of material.

Learn more about calculating linear footage. If your molding is sold in 8′ pieces, then you need to find the number of pieces needed to complete your project. To do this, divide the linear footage measurement by 8 and round up, e.g. (perimeter / 8).

Because joints in trim are undesirable, it may be worth purchasing a little extra trim to account for cuts and waste material to ensure that you can use longer pieces when needed. This is a judgment call that you will need to make based on your room.

Many times, people will purchase one extra piece of molding to have on hand for this reason or in case of future repairs.

Calculate Door and Window Casing

For example, if you’re installing a 3″ thick molding on a 36″ x 48″ window, use the following equation to find how much trim is needed:

This window could technically be completed using two 8′ pieces of molding, but most likely will require three 8′ pieces to accommodate offcuts and using complete sections for each edge. As with base molding, consider that longer lengths should be used to avoid joints when possible, which may require purchasing additional material.