How Many Calories Should a Skinny Guy Eat to Build Muscle?

Struggling to gain size as a skinny guy? Learn how many calories you need to eat to build muscle, with a simple calculation that actually works.

If you’re naturally skinny, building muscle comes down to one thing:

You need to be eating in a consistent calorie surplus. Not just for a day or two, but for weeks.

Here’s how to work it out step by step.

Step 1: Multiply Your Bodyweight by 33–38

Use this formula to estimate how many calories you should eat daily:

Bodyweight (kg) × 33–38 = Daily Calories

• Start with 33 if you’re brand new to training.

• Use 36–38 if you’re already lifting and not seeing the scale move.

📌 Example:

If you weigh 65kg and you’re not gaining weight at 33×, try bumping up to 36–38×.

65 × 36 = 2,340 kcal per day

This is just a starting point. If you’re not gaining after 2 weeks, add 100–150 kcal and re-check.

Step 2: Prioritise Protein 🍗

Muscle is made from protein. Without enough of it, the extra calories you eat can turn into fat instead of size.

📌 Use this:

Bodyweight (kg) × 2g = Daily protein target

Example:

65kg × 2

= 130g of protein per day

Eat a source of protein in every meal - meat, eggs, protein powder, Greek yogurt, etc. And track it.

If you are unsure how many calories, how much protein or what macro split you actually need, nutrition coaching and macro plans can give you personalised targets based on your bodyweight, lifestyle and muscle-building goals.

Step 3: Be Consistent for Weeks, Not Days 📆

Muscle takes time to build. Most skinny guys fail because they give up after 1–2 weeks of “eating more” without tracking anything.

You should be:

✅ Hitting your calorie and protein targets daily

✅ Tracking your weight weekly (not daily)

✅ Sticking to the same training program for at least 4–6 weeks

Consistency becomes much easier when your food intake and workouts are working towards the same goal. Training and nutrition coaching can help align your calorie targets with a progressive training approach so you know exactly what to focus on each week.

What If You’re Still Not Gaining?

Here are 3 quick fixes if the scale won’t budge:

1. Add a liquid meal - like a smoothie or shake; easier to digest. 🥤

2. Increase portion sizes slightly - instead of adding extra meals.

3. Double-check your tracking - are you really eating as much as you think?

Muscle Gain Is a Process. But It Works.

If you’re frustrated by how slow it feels to gain weight, just remember:

Eat slightly more than your body needs.

Train consistently.

Let time do the work. ⏳

Most skinny guys fail because they give up too early, jump between programs, or don’t track what’s working. Don’t make the same mistake.

Want Personalised Help?

I coach naturally skinny guys who want to gain size without turning into a blob. If you’re tired of guessing your calories, tracking aimlessly, and not seeing results…

✅ I’ll calculate exactly what you need

✅ Build a plan that fits your lifestyle

✅ And coach you through every step of the process

Still guessing how much you should be eating or why your weight is not moving? Book a Growth Lab strategy session to identify what is holding back your progress and get clear direction on your nutrition, training and next steps.