# ADU Size Guide: From Studio to 2-Bedroom
The right ADU size depends on who's using it and how much you want to spend - not on building the biggest thing your lot allows. A 500 sq ft one-bedroom ADU handles most use cases beautifully and costs $180,000-$250,000. Going bigger (700-1200 sq ft) costs significantly more but doesn't always generate proportionally more rent or value. Most homeowners end up happier with a well-designed smaller ADU than a cramped larger one.
Let's look at what actually fits and works at each size, with real costs and real use cases.
## Studio ADUs: 300-500 sq ft
**Who this works for:**
- Single person or couple without kids
- Aging parent who downsized possessions
- Young professional or graduate student tenant
- Home office that occasionally hosts overnight guests
- Short-term rental in tourist areas
- Single person or couple without kids
- Aging parent who downsized possessions
- Young professional or graduate student tenant
- Home office that occasionally hosts overnight guests
- Short-term rental in tourist areas
**What fits inside:**
- Combined living/sleeping area (250-350 sq ft)
- Full kitchen or kitchenette (50-80 sq ft)
- Full bathroom (40-60 sq ft)
- Closet/storage (30-50 sq ft)
- Combined living/sleeping area (250-350 sq ft)
- Full kitchen or kitchenette (50-80 sq ft)
- Full bathroom (40-60 sq ft)
- Closet/storage (30-50 sq ft)
**Real layout example (400 sq ft):**
Enter into open living space with murphy bed or sleeping alcove. Kitchen along one wall with full appliances. Separate bathroom. Small closet. One or two large windows for natural light.
Enter into open living space with murphy bed or sleeping alcove. Kitchen along one wall with full appliances. Separate bathroom. Small closet. One or two large windows for natural light.
**Cost range:** $120,000-$180,000 depending on location and finishes
**What homeowners say:**
"Our 450 sq ft studio ADU is perfect for my mom. Open plan makes it feel bigger than it is. She has everything she needs and loves the simplicity." - Seattle homeowner
"Our 450 sq ft studio ADU is perfect for my mom. Open plan makes it feel bigger than it is. She has everything she needs and loves the simplicity." - Seattle homeowner
**Rental income:** $1,000-$1,600/month depending on market
**The limitations:**
Limited privacy between sleeping and living areas. Tight for couples who both work from home. Storage is minimal. Not ideal for families with kids or anyone with lots of belongings.
Limited privacy between sleeping and living areas. Tight for couples who both work from home. Storage is minimal. Not ideal for families with kids or anyone with lots of belongings.
**Sweet spot:** 400-450 sq ft gives you proper bathroom, real kitchen, and living space that doesn't feel cramped.
## One-Bedroom ADUs: 500-700 sq ft
**This is the most popular size** - the Goldilocks option that works for the widest range of uses.
**Who this works for:**
- Single person or couple who want privacy
- Aging parent with some furniture/belongings
- Small family (couple + infant/toddler)
- Professional tenant paying market rent
- Teen/young adult who needs their own space
- Combination home office + guest suite
- Single person or couple who want privacy
- Aging parent with some furniture/belongings
- Small family (couple + infant/toddler)
- Professional tenant paying market rent
- Teen/young adult who needs their own space
- Combination home office + guest suite
**What fits inside:**
- Living room (150-200 sq ft)
- Bedroom with closet (100-150 sq ft)
- Kitchen (60-100 sq ft)
- Full bathroom (40-60 sq ft)
- Entry/circulation (50-80 sq ft)
- Optional: small porch or deck
- Living room (150-200 sq ft)
- Bedroom with closet (100-150 sq ft)
- Kitchen (60-100 sq ft)
- Full bathroom (40-60 sq ft)
- Entry/circulation (50-80 sq ft)
- Optional: small porch or deck
**Real layout example (600 sq ft):**
Front door opens to living/kitchen area (250 sq ft combined). Hallway leads to separate bedroom with closet (120 sq ft) and bathroom (50 sq ft). Feels like a real apartment, not a converted garage.
Front door opens to living/kitchen area (250 sq ft combined). Hallway leads to separate bedroom with closet (120 sq ft) and bathroom (50 sq ft). Feels like a real apartment, not a converted garage.
**Cost range:** $180,000-$250,000
**What homeowners say:**
"We built 650 sq ft with a separate bedroom. My in-laws have privacy when they visit, and when we rent it out, tenants stay 2-3 years because it's actually livable long-term." - Austin homeowner
"We built 650 sq ft with a separate bedroom. My in-laws have privacy when they visit, and when we rent it out, tenants stay 2-3 years because it's actually livable long-term." - Austin homeowner
**Rental income:** $1,400-$2,200/month depending on market
**Why this size works so well:**
- Genuine bedroom separation creates privacy
- Enough room to not feel cramped
- Appeals to widest range of tenants
- Cost is manageable but delivers full functionality
- Adds substantial home value
- Genuine bedroom separation creates privacy
- Enough room to not feel cramped
- Appeals to widest range of tenants
- Cost is manageable but delivers full functionality
- Adds substantial home value
**Design tip:** 600 sq ft is the sweet spot. Going from 500 to 600 sq ft makes a huge livability difference. Going from 600 to 700 sq ft is nice but not transformative.
## Large One-Bedroom: 700-850 sq ft
**Who needs this size:**
- Couple who wants spacious living
- Someone working from home who needs dedicated office space
- Aging parent with significant furniture/belongings
- Family with one young child
- Multi-generational living with shared time in ADU
- Couple who wants spacious living
- Someone working from home who needs dedicated office space
- Aging parent with significant furniture/belongings
- Family with one young child
- Multi-generational living with shared time in ADU
**What the extra space gets you:**
- Larger living room or separate dining area
- Walk-in closet in bedroom
- Bigger kitchen with island or breakfast bar
- Laundry closet (washer/dryer)
- Larger bathroom or powder room + full bath
- Covered porch
- Larger living room or separate dining area
- Walk-in closet in bedroom
- Bigger kitchen with island or breakfast bar
- Laundry closet (washer/dryer)
- Larger bathroom or powder room + full bath
- Covered porch
**Cost range:** $220,000-$300,000
**Rental income:** $1,600-$2,400/month
**The tradeoff:**
You're paying 25-35% more than a 600 sq ft ADU but typically don't get 25% more rent. Makes more sense for family use than pure rental investment.
You're paying 25-35% more than a 600 sq ft ADU but typically don't get 25% more rent. Makes more sense for family use than pure rental investment.
**When it's worth it:**
If someone will live there long-term (parent, adult child, you eventually), the extra comfort is worth the cost. For short-term rentals where space matters less, probably not worth it.
If someone will live there long-term (parent, adult child, you eventually), the extra comfort is worth the cost. For short-term rentals where space matters less, probably not worth it.
## Two-Bedroom ADUs: 800-1,200 sq ft
**Who needs this size:**
- Small family (parents + 1-2 kids)
- Multi-generational living (grandparent + caregiver)
- Two roommates sharing rent
- Guest house that hosts multiple visitors
- Primary residence while renting out main house
- Small family (parents + 1-2 kids)
- Multi-generational living (grandparent + caregiver)
- Two roommates sharing rent
- Guest house that hosts multiple visitors
- Primary residence while renting out main house
**What fits inside (1,000 sq ft example):**
- Living room (200 sq ft)
- Kitchen (120 sq ft)
- Bedroom 1 (120 sq ft)
- Bedroom 2 (100 sq ft)
- Bathroom 1 (50 sq ft)
- Bathroom 2 (optional, 40 sq ft)
- Hallway/circulation (100 sq ft)
- Storage/laundry (60 sq ft)
- Living room (200 sq ft)
- Kitchen (120 sq ft)
- Bedroom 1 (120 sq ft)
- Bedroom 2 (100 sq ft)
- Bathroom 1 (50 sq ft)
- Bathroom 2 (optional, 40 sq ft)
- Hallway/circulation (100 sq ft)
- Storage/laundry (60 sq ft)
**Cost range:** $250,000-$350,000+
**Rental income:** $1,800-$3,000/month
**What homeowners say:**
"We built 1,100 sq ft with 2 bedrooms and 1.5 baths. It's essentially a small house. Our adult daughter and her husband live there while saving for their own home. Worth every penny for family, but wouldn't have built this big for rental only." - Denver homeowner
"We built 1,100 sq ft with 2 bedrooms and 1.5 baths. It's essentially a small house. Our adult daughter and her husband live there while saving for their own home. Worth every penny for family, but wouldn't have built this big for rental only." - Denver homeowner
**The math challenge:**
A 1,000 sq ft two-bedroom might cost $280,000 but only rent for $2,200/month. A 600 sq ft one-bedroom might cost $200,000 and rent for $1,700/month. You're paying $80,000 more for $500/month more rent - a longer payback period.
A 1,000 sq ft two-bedroom might cost $280,000 but only rent for $2,200/month. A 600 sq ft one-bedroom might cost $200,000 and rent for $1,700/month. You're paying $80,000 more for $500/month more rent - a longer payback period.
**When it makes sense:**
- Family use where comfort and space matter more than ROI
- High-rent markets where two-bedroom premium is significant
- Lot is large enough that going bigger doesn't sacrifice yard space
- Long-term plan includes potential resale value (buyers love two-bedroom ADUs)
- Family use where comfort and space matter more than ROI
- High-rent markets where two-bedroom premium is significant
- Lot is large enough that going bigger doesn't sacrifice yard space
- Long-term plan includes potential resale value (buyers love two-bedroom ADUs)
## How Size Affects Cost Per Square Foot
Smaller ADUs cost more per square foot due to fixed costs:
- 400 sq ft studio at $160K = $400/sq ft
- 600 sq ft one-bedroom at $210K = $350/sq ft
- 1,000 sq ft two-bedroom at $300K = $300/sq ft
- 600 sq ft one-bedroom at $210K = $350/sq ft
- 1,000 sq ft two-bedroom at $300K = $300/sq ft
Kitchen, bathroom, and utility connections cost roughly the same regardless of ADU size. The marginal cost of adding square footage is mostly structure and finishes, which is cheaper.
**But:** Total cost still matters more than cost per square foot. Spending $300K on a two-bedroom might make sense for your family but be a poor investment compared to $210K on a one-bedroom that generates nearly as much rent.
## Local Size Restrictions
Many cities have maximum ADU sizes:
- **Portland:** 800 sq ft max
- **California (most cities):** 850-1,200 sq ft max depending on lot size
- **Seattle:** 1,000 sq ft max
- **Denver:** 125% of main house footprint or 1,000 sq ft, whichever is less
- **Portland:** 800 sq ft max
- **California (most cities):** 850-1,200 sq ft max depending on lot size
- **Seattle:** 1,000 sq ft max
- **Denver:** 125% of main house footprint or 1,000 sq ft, whichever is less
Check your local rules before falling in love with a large floor plan. Your builder will know the limits.
## The "Finished Basement" Comparison
A 600 sq ft one-bedroom ADU costs $180,000-$250,000. That sounds expensive until you realize:
- Finished basement in existing home: $100-$150/sq ft = $60,000-$90,000 for 600 sq ft
- ADU: $300-$400/sq ft = $180,000-$240,000 for 600 sq ft
- ADU: $300-$400/sq ft = $180,000-$240,000 for 600 sq ft
But the ADU:
- Has its own entrance, kitchen, and bathroom
- Generates rental income ($1,400-$2,200/month)
- Adds more home value ($100,000-$200,000)
- Functions as completely independent housing
- Has its own entrance, kitchen, and bathroom
- Generates rental income ($1,400-$2,200/month)
- Adds more home value ($100,000-$200,000)
- Functions as completely independent housing
You're paying more because you're getting a separate dwelling unit, not just finished space.
## Making Your Size Decision
**Start with your use case:**
**For aging parents:** 500-700 sq ft one-bedroom. They need privacy and full amenities but not excessive space.
**For adult children:** 400-600 sq ft. Young adults often prefer cozy, affordable over large and expensive.
**For rental income:** 500-650 sq ft one-bedroom. Sweet spot for rent-to-cost ratio.
**For short-term rental:** 400-600 sq ft. Guests prioritize location and amenities over space.
**For multi-generational living:** 700-1,000 sq ft with two bedrooms. Worth the cost for long-term family use.
**For flexibility:** 600 sq ft one-bedroom. Works for nearly any future use case.
## Don't Build For Someday
Many homeowners are tempted to build bigger "just in case" or "for resale value." But:
- Every square foot costs real money now
- You're paying interest on that larger loan
- Larger ADU = higher property taxes forever
- Most future buyers want ADUs 600-800 sq ft anyway
- You're paying interest on that larger loan
- Larger ADU = higher property taxes forever
- Most future buyers want ADUs 600-800 sq ft anyway
**Build for your actual need** with a small buffer. If your parent needs 500 sq ft, building 600 sq ft makes sense. Building 900 sq ft "in case they need it" means you're paying for space they won't use.
## The Right Size Is Personal
Unlike cost per square foot or rental rates, which follow market logic, size is deeply personal. A minimalist couple might thrive in 450 sq ft while someone else feels cramped in 700 sq ft.
**Best next step:** Look at actual floor plans in your target size range [builder directory link]. You'll quickly know if a space feels right or too small. Photos and virtual tours help you visualize far better than square footage numbers.
Many homeowners find that 600 sq ft feels perfect, 500 sq ft feels tight but workable, and 400 sq ft requires careful design. But the only way to know your threshold is to look at real examples.
Check if your property qualifies for an ADU [property checker link], then explore floor plans from builders who've perfected efficient layouts at each size. The right size becomes obvious when you see how the space actually flows.