Umberto the first ruled the Kingdom of Italy from 1878 to 1900 and many coins were issued with his likeness. The 20, 50, and 100 lire were issued in gold, as follows:
20 lire: 21 mm diameter, 0.1867 troy ounces gold
50 lire: 28 mm diameter, 0.4667 ounces gold
100 lire: 34 mm diameter, 0.9334 ounces gold
Note that 'troy' is understood when you are talking about 'ounces' of precious metal.
The 50 and 100 lire coins are quite rare. You can see an appraisal of a 50 lire piece at this CoinQuest link. Watch out for counterfeits, as shown on this page.
The 20 lire coins are best evaluated in two steps. First, multiply their gold weight by the current price of gold. For instance, if gold is selling at $1420 US dollars per ounce (refer to kitco.com for the current value), the multiplication is 1200 x 0.1867 = $265. This is the basic gold value, often called the melt value.
20 lire coins in well worn condition, or ones with problems like scratches and stains, or having been used in jewelry, are worth the melt value. But collector demand lifts off zero for nice-looking coins. I'd add about $50 for an average circulated coin, and as much as $100 or more to the melt value for a nice uncirculated specimen to get ballpark retail value. If you want to sell one, figure a dealer will pay about 80 percent of melt plus a few dollars collector premium.
NEVER CLEAN A COIN. CLEANING RUINS VALUE.
Now there is another twist if you have a 20 lire dated 1884 or 1889. These are special dates and the collector premium doubles or triples. Hope you have one!