What's worth more, your money or your time?

The adage is time is money, but how much money is it really worth?

Every day we make snap judgments about the value of our time. We pay an accountant rather than doing our own taxes. We hire a house cleaner rather than cleaning up after ourselves. We use a valet rather than circling the block for a parking space.

''Most people don't explicitly think about it. They just sort of guess, make a rough judgment," said Donald B. Rosenfield, a senior lecturer at the MIT Sloan School of Management.

Yet there are more precise ways to measure the value of an individual's leisure time. Most of them are extrapolations from what a person earns at work. The higher an individual's pay, the more valuable their leisure time is.

Philosophical considerations enter in. Some time-value calculators say a person's leisure time has the same value as their hourly salary, or even less. Others say leisure time is far more valuable than work time, as much as two to three times hourly pay.

Samuel Blackman of Jamaica Plain is a person who has been able to quantify the value of his leisure time exactly. Blackman works as an oncology fellow in pediatrics, splitting his time between the Dana-Farber Cancer Institute and Children's Hospital. It's a job that involves long hours and low pay.

But he discovered that many other hospitals and clinics needed his pediatric skills, and were willing to pay him roughly seven times as much an hour if he were willing to moonlight -- and he does. So, his leisure time is now a precious commodity and he treats it that way.

''For me, spending six hours cleaning house on a Saturday is not worth it. I never wash my car by hand or change the oil myself," he said.

Blackman says he now understands why his superiors grimace when he asks for five minutes of their time. ''Everyone wants five minutes of their time, and that time is incredibly valuable," he said. ''The higher up the food chain you get, the more valuable your time is."

A report released earlier this month on the benefits of the Big Dig suggested just how valuable time can be. The report, prepared for the Massachusetts Turnpike Authority by the Economic Development Research Group of Boston, said the Big Dig is saving area residents and businesses travel time worth $142.6 million a year.

The travel time of a working person was valued at $26.68 an hour, the average wage rate. The travel time of someone who wasn't working -- driving to the Museum of Science or heading to Fenway Park -- was valued at $13.34 an hour, half the hourly wage.

Glen Weisbrod, president of the group and an authority on time-value analysis, said $13.34 an hour is an accepted standard nationally for the value of a typical individual's time.

''It's what people would be willing to pay to use their time a different way," he said.

Paul English, the chief technology officer at Kayak Inc., said time savings are so important to consumers that the company has toyed with incorporating time into its travel search engine product.

English said one version of Kayak's software lets users enter the value of their time on a per-minute basis. A travel search then ranks flights by price, including the cost of layovers. With that approach, a one-stop flight that is $50 cheaper may not really have a lower cost if the traveler's layover time is included.

''The thing that I realize as I get older, and as I witnessed the death of my parents, is to try to focus on every minute," English said. ''You don't need to get to the end of your life to wish for another hour or minute with a loved one. You can think about that every day."

But few people view their time as a precious commodity or in strictly economic terms; many have quirks in how they parcel their time. Rosenfield, the MIT lecturer, said that as long as the cost is not exorbitant, he is willing to pay if he can save more of his personal time. But for some reason he draws the line at paying a parking valet.

''I don't like valet parking as a matter of course," he said.

Michael Norton, assistant professor of marketing at Harvard Business School, said most people would assume it was cost-effective to pay someone else to do something if it would save them time. But his research has shown just the opposite in some cases.

One of his experiments involved having people make origami and then compare their creations to those made by someone who excels at origami. What Norton found was that people would wildly overvalue the origami they had made, even if it wasn't very good, because they spent the time making it.

Norton calls it the ''Ikea effect" because he's found that shoppers who assemble furniture purchased at the Swedish big box store seem to value the furniture more than it's really worth.

The value of an individual's time varies with the weather, the person's mood, or even the day of the week, Norton says. ''It's not an economic calculation that people are making," he said. ''The feeling is you'll use it for something productive, but that's unlikely. You may just watch TV."

Bruce Mohl can be reached at mohl@globe.com.