Find out the materials needed to complete your home repair job. If you're replacing a damaged floor with new tile, for example, you'll need the tile itself as well as any required materials to install the title (which will change based on the nature of the job). To fix the insulation around the windows in your home, you will need new insulation material like caulking. Write down all your required materials.
Go through the list of materials from Step 1 and find prices for everything you wrote down. If you need new tile, for example, go to a hardware store and price out the tile you'll need. You can also find this information online for materials and tools that are sold over the Internet. If you have to rent or buy a specific tool to complete your home repair job, write down the cost of renting or buying the tool in question. If you're not sure what you need to do a specific job, ask an expert.
Factor in man-hours. If you're creating an estimate for someone else on work you will be completing, look over the job and try to determine how long it will take you to complete. Then, multiply your hourly rate by the number of hours it will take you to finish your work. If you're hiring your own contractor, multiply their hourly rate by the number of hours it will take them to complete the job. In both situations, it may also be possible to negotiate a flat fee for service (which means there is one price, no matter how long it takes), but that will depend on the contractor or your own preferences (if you are the contractor).
Add up your cost of materials and your cost for labor. The price you are left with is a reasonable, ballpark estimate for how much it will take to finish a home repair job.