San Francisco is 4.7°C (8.5°F) warmer by day, San Francisco has 5°C (9°F) warmer nights, Boston gets 594 mm (23.4 in) more rain a year.
Boston is at its warmest in July and coolest in January, while San Francisco peaks in September and bottoms out in January. Month for month, San Francisco is the warmer of the two in 9 of 12 months.
Boston is the wetter of the two, collecting 1,213 mm (47.8 in) of rain a year against 619 mm (24.4 in) in San Francisco. The most comfortable time to visit is June, July and August in Boston and July, August and September in San Francisco.
| Boston | Metric | San Francisco |
|---|---|---|
| 🌡️ Temperature | ||
| 57.4°F | 🌡️Average daytime high | 65.8°F |
| 40.1°F | 🌙Average nighttime low | 49.1°F |
| July | 🔥Hottest month | September |
| January | ❄️Coldest month | January |
| 🌧️ Rain | ||
| 47.8 in | 🌧️Annual rainfall | 24.4 in |
| October | ☔Wettest month | December |
| February | 🏜️Driest month | July |
| 💨 Climate | ||
| 80% | 💧Average humidity | 77% |
| 0.7 m/s | 💨Average wind speed | 2.3 m/s |
Overnight, Boston typically falls to around 4.5°C (40.1°F) while San Francisco settles near 9.5°C (49.1°F).
Boston is hottest in July and coldest in January, whereas San Francisco peaks in September and is coolest in January.
Boston sees the most rain in October and the least in February; San Francisco is wettest in December and driest in July.
Boston feels the more humid of the two, averaging 80% relative humidity against 77%.
For San Francisco, the pick of the year is July, August and September.
Month by month, here is the coldest night, the average day and the hottest afternoon each city can expect. Switch Compare to read rainfall, humidity, wind or solar instead, and Period to move between the long-term 45-year average and any single year — the shading is a quick warm-to-cool guide.
| Month | Boston | San Francisco | ||||
|---|---|---|---|---|---|---|
| Min | Avg | Max | Min | Avg | Max | |
| January | 17.8 | 25❄️ | 32.4 | 43.3 | 49.8❄️ | 56.3 |
| February | 19.4 | 27.1 | 34.9 | 44.6 | 51.3 | 57.9 |
| March | 26.4 | 34.7 | 43 | 46 | 52.9 | 59.9 |
| April | 35.8 | 45.1 | 54.5 | 47.1 | 55 | 63 |
| May | 46.4 | 55.9 | 65.5 | 49.6 | 58.3 | 66.9 |
| June | 55.9 | 65.1 | 74.3 | 52 | 61.7 | 71.2 |
| July | 62.4 | 71.8🔥 | 81.1 | 53.6 | 63.3 | 73 |
| August | 61.3 | 71.1 | 80.8 | 54.9 | 64.8 | 74.5 |
| September | 54.1 | 64 | 73.8 | 55.2 | 65.3🔥 | 75.4 |
| October | 43.7 | 52.5 | 61.5 | 52.9 | 62.2 | 71.6 |
| November | 33.8 | 41.5 | 49.3 | 47.7 | 55.2 | 62.8 |
| December | 24.8 | 31.5 | 38.1 | 43.5 | 50 | 56.5 |
| Annual Avg | 40.1 | 48.7 | 57.4 | 49.3 | 57.6 | 65.7 |
Min / mean / max temperature (°F). 🔥 marks each city's hottest month, ❄️ its coldest; shading runs cool blue to warm red.
The same figures plotted out, so the shape of a typical year is easier to see than in a grid. Where the two lines run close together Boston and San Francisco feel alike; where they separate, they are genuinely different places to be.
Hover or tap any point to read the exact figures. Boston San Francisco
See how Boston and San Francisco stack up against other cities. Swipe for more.
Choose which city to keep, then search for any other city in our database — we'll build the comparison for you.
Quick answers to the questions people ask most when comparing Boston and San Francisco — each drawn straight from the climate figures above.
San Francisco is the warmer of the two. It averages daytime highs of 18.8°C (65.8°F) against 14.1°C (57.4°F) in Boston — roughly 4.7°C (8.5°F) warmer by day. Nights are milder in San Francisco, with average lows of 9.5°C (49.1°F) versus 4.5°C (40.1°F).
Boston is hottest in July, averaging highs of about 27.3°C (81.1°F), while San Francisco peaks in September at around 24.1°C (75.4°F). That makes Boston the hotter of the two at the height of summer.
Boston gets colder. In its coldest month (January) overnight lows average about -7.9°C (17.7°F), compared with 6.3°C (43.3°F) at the low point of the year in San Francisco.
Boston is the wetter city, collecting about 1,213 mm (47.8 in) of rain a year versus 619 mm (24.4 in) in San Francisco. Boston is wettest in October and driest in February; San Francisco is wettest in December and driest in July.
Boston is the more humid of the two, averaging 80% relative humidity over the year against 77% in San Francisco.
The most comfortable months in Boston are June, July and August, when average temperatures are at their mildest.
San Francisco is at its most pleasant around July, August and September, based on the mildest average temperatures of the year.
San Francisco is the warmer city in 9 of the 12 months of the year. The gap is widest in January, about 13.8°C (24.8°F), and narrowest in September, about 0.7°C (1.3°F).
Boston has the bigger seasonal swing, about 26°C (46.8°F) between its coldest and hottest months versus 8.6°C (15.5°F) in San Francisco — so San Francisco has the steadier, more even climate.
On climate alone, San Francisco comes out ahead — it offers warmer days, less rain and lower humidity than Boston. Boston is the better fit only if you'd actually prefer cooler weather, more rainfall and a more humid climate.
Every figure on this page is calculated from NASA POWER satellite climate data spanning 1981–2025 (45 years). The averages describe the long-term climate of Boston and San Francisco, not a single year's weather or a short-range forecast.
